I recall reading somewhere that Montezuma told Cortes something along the lines of "you left the mother land more recently than us." How much truth is there to this?
Montezuma didn't have knowledge of the bering strait, so no. Here is an article from the faq discussing trade routes of pre Colombian Americas https://www.reddit.com/r/AskHistorians/comments/1o734s/how_extensive_were_the_north_american_trade/
More directly addressing op question https://www.reddit.com/r/AskHistorians/comments/1nd1m2/were_native_americans_aware_of_other_tribes/
The best answer would be that "No he did not know", however depending on what side of the debate you fall on, there was some belief that the Mexica came from Southwest US. How accurate that statement is really still up to debate. On the Humboldt map I forget what year, there was this place city marked on it that was referred to as the ancient in reference to the Mexica people however there is no physical evidence of the existence of this place as far as we know. My adviser was on the fringe, and hearing him talk about it was little crazy. Oh I should probably mention that it was not unusually for map makers to put false things sorta as an early plagiarism detector, so it could purely have been that. Though the Mexica according to their belief, thought they were from somewhere else but they weren't quite sure where there are descriptions of that place
Haha, no. There's no way for him to know, either.
If the quote was indeed genuine, then he was probably referring to the fact that the Aztecs were relative newcomers to Mesoamerica; migrating from the northern deserts of Mexico and taking over the political sphere from there.