zlacker

The assumption is the acceleration and the gravitation are in the same direction and the same magnitude. The point is that given these two, it's impossible to distinguish the two.

If you think it's sneaky to "implicitly" assume they're in the same direction, I would point out that this is no different from assuming they have the same magnitude. It would be kinda dumb to say "well this 1m/s^2 acceleration can't possibly be equivalent to gravity because gravity is 9.8m/s^2, so the statement is obviously wrong and they're trying to trick me!!"... same thing for direction.