There are two consecutive Mishnayos in Pirkei Avos that use the phrase "מעלה עליו הכתוב", which loosely translates to 'scripture treats him as...'
The first is:
רַבִּי שִׁמְעוֹן אוֹמֵר, הַמְהַלֵּךְ בַּדֶּרֶךְ וְשׁוֹנֶה, וּמַפְסִיק מִמִּשְׁנָתוֹ וְאוֹמֵר, מַה נָּאֶה אִילָן זֶה וּמַה נָּאֶה נִיר זֶה, מַעֲלֶה עָלָיו הַכָּתוּב כְּאִלּוּ מִתְחַיֵּב בְּנַפְשׁוֹ
Rabbi Shimon says if one is studying while walking on the road and interrupts his study and says, “how fine is this tree!” [or] “how fine is this newly ploughed field!” scripture accounts it to him as if he was mortally guilty.
This mishna does not mention any scriptural source for the 'mortal guilt' assigned to the person who did these things.
The second mishna that uses this phrase does quote a verse from scripture, but there is no clear assignment of 'mortal guilt' in the verse, just that this something prohibited:
רַבִּי דּוֹסְתַּאי בְּרַבִּי יַנַּאי מִשּׁוּם רַבִּי מֵאִיר אוֹמֵר, כָּל הַשּׁוֹכֵחַ דָּבָר אֶחָד מִמִּשְׁנָתוֹ, מַעֲלֶה עָלָיו הַכָּתוּב כְּאִלּוּ מִתְחַיֵּב בְּנַפְשׁוֹ, שֶׁנֶּאֱמַר (דברים ד) רַק הִשָּׁמֶר לְךָ וּשְׁמֹר נַפְשְׁךָ מְאֹד פֶּן תִּשְׁכַּח אֶת הַדְּבָרִים אֲשֶׁר רָאוּ עֵינֶיךָ
Rabbi Dostai ben Rabbi Yannai said in the name of Rabbi Meir: whoever forgets one word of his study, scripture accounts it to him as if he were mortally guilty, as it is said, “But take utmost care and watch yourselves scrupulously, so that you do not forget the things that you saw with your own eyes” (Deuteronomy 4:9).
So my question is as follows:
Does מעלה עליו הכתוב mean that there is a verse backing it up (indication being that this isn't the case, based on the source above) and if it doesn't, then what does it mean?