Now, I assure you, we're thinking the exact same things you're thinking: these stats are totally bunk, anyone can edit their computer ID to be listed as anything they want, and one stat on Adium's page does not mean that Apple is coming out with some sort of revolutionary miniature laptop. And we agree with you -- it's almost certainly nothing of consequence. Or, that is, we would completely agree with you, except for one thing: it's happened exactly this way before. A little computer called the MacBook Air first showed up in Adium's stats, and people argued those exact same things at the time, and it all turned out to be real.
You might say that makes it doubly likely for someone to tweak their computer's settings to show up as some legendary Apple test machine, and again, we'd agree with you. But it's a big world out there -- unless you work at 1 Infinite Loop, you have no idea what Apple is testing and working on right now. Like I said, we just thought we'd let you know. Just in case.