I've never heard of the first reason. The reason the gemarra gives is similar to your second reason, which is probably what you are thinking of, although it's phrased differently than you bring it:
הָתָם גַּבְרָא בַּר חִיּוּבָא הוּא, וְרַבָּנַן הוּא דְּלָא אַטְרְחוּהוּ מִשּׁוּם כְּבוֹד שַׁבָּת
There, on Shabbat, the individual is one who is obligated and should actually recite all eighteen blessings, and it is the Sages who did not impose upon him in deference to [the honor of] Shabbat and instituted an abridged formula.
If you understand כבוד שבת/the honor of Shabbos as meaning saying Kiddush quickly, then it's the same as what you heard. However, I'm personally not sure what it means they shortened shemoneh esrei for the honor of Shabbos. I wouldn't think it means so you can make Kiddush quickly.