Or HaChaim on Genesis 19:3/אור החיים על בראשית י״ט:ג׳

1 ויעש להם משתה. He prepared a feast for them. The correct meaning of the verse is that while Lot prepared a meal for them the angels ate only matzot. This was because Lot did not observe the commandments of the Torah as did Abraham. At Abraham's home the angels had no compunction about eating meat. The angels either knew that Lot had tithed the flour he used for baking the matzot, or they reasoned that in the absence of priests to give the tithe (תרומה) to, they assumed that function themselves and ate the part which could be considered terumah whereas they did not eat the regular matzah. According to our sages (Midrash Hagadol), the date was the 16th of Nissan and Lot had baked matzah in anticipation of the eventual Passover holiday some 400 years hence.