As a general rule, I wouldn't take what any campaign says at face value, and the Trump people are so obviously liars and leakers that I wouldn't trust them to tell me what 1+1 is.

Best guess, Harris is doing some kind of "messaging" event (like unions or something), is tying this event in with a fundraiser, or simply wants to hit New England to help shore up the region (even if it's likely we win every EV save one of Maine's) or to make a point that it's not being neglected (I'm not cognizant of her other campaign stops, honestly).