Criticism isn’t necessarily condescending. “You should be doing x because y” is just a plain assertion, it doesn’t imply any moral judgement or opinion of the author.
I don't necessarily read it as condescending, but I do read it as presumptuous. What someone "should" do depends on many things. Maybe, because this is software in alpha stage, they should _not_ focus on this part of the code if it is minor compared to other obligations. Or maybe there are other reasons they've chosen not to do this (as was explained in an above comment).
IMO, a less presumptuous criticism would be phrased like "if you did X then benefits Y would happen", or "if you haven't, consider X", or even (the least presumptuous - make it a conversation!) "have you considered X?", rather than "you should do X".
I see what you mean. Perhaps it was just a "poor" choice of words for whatever reasons. I am sure we can assume he intended it in a way of "have you considered X?".
