In Parashat Vayera, we read that Lot gives the angels matzah (19:3). Rashi's explanation for this detail is that it was Pesach. The connection between matzah and Pesach is obvious, but I am confused as to why we can say that they observed Pesach at all at this point chronologically.
My understanding is that Pesach is about the exodus from Egypt, which has yet to happen. One might argue that Pesach was simply a pre-existing festival that was later endowed with greater meaning, but I find that doubtful. Moreover, matzah is eaten because there was no time for bread to rise when the Jews went out of Egypt (this is attested in numerous places, including Deut. 16:3), and this has not happened yet, so either way, I do not see why they would eat it.
How exactly is this supposed to be rationalized? Or is this supposed to simply be a coincidental prefiguration of Pesach in some shape or form?