Well I know with Curtis his speech has always been a little off although we are seeing improvements. I think kids do say things thinking other things, if that makes sense! He also may look at you as a mom figure at times, or even just get confused in the moment.
One thing that I would suggest is correcting him. I think it's a special title for his mom and even though he doesn't mean anything by it, it can hurt a mom when someone else is called mom by your own kid (I know for me it does). If you say "Sure, Aunty Micky will get it for you" or whatever, this will help him to get the correct term in to his little head!
he's still so young

Dustin still screaming and babbling so it just comes with time to get the right term for the right thing! Just keep on reminding him!