What do the words "מוריד הטל" mean? Dew does not "fall" or "come down".
Also what do the words "ותן טל...לברכה" mean? What is an example of טל not לברכה?
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Your 2nd question is interesting. The "problem" is that you are thinking of "dew" as the common liquid form that you see during the spring and summer, mainly. That's commonly called "dew". You need to think a bit more broadly. Wikipedia says:
Dew is water in the form of droplets that appears on thin, exposed objects in the morning or evening due to condensation. As the exposed surface cools by radiating its heat, atmospheric moisture condenses at a rate greater than that at which it can evaporate, resulting in the formation of water droplets.
When temperatures are low enough, dew takes the form of ice; this form is called frost.
So, frost is actually dew that freezes on contact with the cold surface. (Technically, dew can also freeze in the air - what's sometimes called "frozen fog".)
If you're a farmer or even just a home plant grower, you know how damaging frost is to plants and herbage. In Israel, I'm sure that if frost develops while produce is growing, it is far from a bracha as this causes significant damage to a huge crop field and farmers can suffer major financial loss overnight.
Alex's answer is more lomdishe as it provides a direct Talmudic citation. So, consider my answer as a "subset". Clearly, frost or rime are types of dew that do not cause plants to grow. Worse - it kills the ones that are growing. Although, amazingly, they can still regrow, in most cases.
Dew as a blessing vs not as a blessing is discussed in the Talmud:
תנא בטל וברוחות לא חייבו חכמים להזכיר ואם בא להזכיר מזכיר מ"ט א"ר חנינא לפי שאין נעצרין וטל מנלן דלא מיעצר דכתיב ויאמר אליהו התשבי מתושבי גלעד אל אחאב חי ה' אלהי ישראל אשר עמדתי לפניו אם יהיה השנים האלה טל ומטר כי אם לפי דברי וכתיב לך הראה אל אחאב ואתנה מטר על פני האדמה ואילו טל לא קאמר ליה מאי טעמא משום דלא דלא מיעצר וכי מאחר דלא מיעצר אליהו אשתבועי למה ליה הכי קא"ל אפילו טל דברכה נמי לא אתי וליהדריה לטל דברכה משום דלא מינכרא מילתא
It has been taught: The Sages did not make it obligatory on one to make mention of dew and winds, but if one desires to make mention he may do so. What is the reason? — R. Hanina said: Because they are never withheld. And how do we know that dew is never withheld? — For it is written, And Elijah the Tishbite, who was of the settlers of Gilead, said to Ahab: As the Lord the God of Israel liveth, before whom I stand, there shall not be dew nor rain these years but according to my word. And it is written further, Go, show thyself unto Ahab, and I will send rain upon the land. Of dew, however, Scripture does not speak. Why? Because it is never withheld. But if it is never withheld, why did Elijah take an oath on it? — This is what he conveyed to him [Ahab]. THe dew of blessing also would not fall. Then the dew of blessing should also have been restored? — Because the difference would not have been discernable. (Soncino translation, my emphasis)
(See also the Mishnah in Sotah 9:13.)
Rashi explains the dew of blessing as:
שיצמיח שום תצח
I.e. dew of blessing is that which causes some form of plant life to grow. It follows, then, that dew that is not for a blessing would be dew that does not cause any plant life to grow.
As for why dew is described as "falling", R. Dr. Natan Slifkin suggests that this may fall into the category of things that are described "in the language of men":
The Question of the Kidneys' Counsel p. 19 (my emphasis)
Accordingly, Orthodox Jews can accept that Scripture speaks of the kidneys as actually providing counsel, and also accept that the kidneys do not in fact do this. Furthermore, this approach has many applications beyond the question of the kidneys’ counsel. Aside from the astronomical and cosmological issues discussed by Rambam, Ralbag, Rav Hirsch and Rav Kook, there are a number of instances where the Scriptures, according to traditional and scholarly interpretation, conflict with modern science.56 While traditionalists struggle to reinterpret these verses and fit them into modern science, the principle of “the Torah speaks in the language of men” as utilized by the aforementioned authorities, while not without its own difficulties, renders these reinterpretations unnecessary.
56. Thus, as well as the inconsistency between the Genesis account of the age and development of the universe, the geocentric description of the universe, and the description of the firmament being a flat, firm structure, there is also the description of dew descending from the heavens and the descriptions of the hare and hyrax as ruminants.