No, it's because of the informal nature of english, I think. In english we really should say "I come in order to eat", or "I come for the purpose of eating", but we shorten it to "I come to eat". There are a lot of occasions where the esperanto translation sounds like a more formal version of modern english.
As far as I can tell, "por" = "for"/"in order to" and not any other meaning of "to".
One could also translate this sentence as "I'm coming for to eat", making the "for" explicit, and it would be perfectly valid English -- same as e.g. "coming for to carry me home" -- but in practice nobody else seems to use that construction in English anymore.