If they took programmers from offices, and made them sit together in a room together all of a sudden, then you might just be measuring how upset programmers get

If they took programmers from offices, and made them sit together in a room together all of a sudden, then you might just be measuring how upset programmers get when you make them move desks! You could probably get the same result in reverse and conclude that less communication hurt productivity. You're changing more than one thing at once, so you can't guarantee a causal relationship between the result and the thing you intended to change.