It's the former; Deanna talks in an age-inappropriate fashion and treats Mike like a piece of crap.
Panel 1: On the bus ride home, Deanna tells the little girl that she's sitting next too that her family had an okay house in Burlington but they couldn't sell the one they had here. This, of course, is a concept that would mean nothing to a real six year old.
Panel 2: So would the next wall of text she delivers; no sixc year old would have noticed that Wilf's old boss had missed him or that he'd go on to ask him to be the manager of a fancy new store; she'd know that Mira said "Yes" to something but not to that thing.
Panel 3: She might possibly, however, tell people that that being back in her old house is cool because she gets to hang out with her old friends.
Panel 4: The only thing that does make any sense is giving Mike the hearty Bronx cheer she does as he passes by; that's because she doesn't consider him to be a friend at all.
Summary: How will Mike react to Deanna's acting like a real six year old? Will he lash out at someone weaker than he is? Will he let that "Blaarrpppffffbbt!" sit is his stomach and fester? Do you care?