As Eddy is taking his clothes off getting ready to jump into the lake, you can clearly see he's wearing underwear and that he drops his T shirt as he begins his run. But in the next scene from behind, Eddy is no longer wearing underwear and again drops his T shirt.
Eddie remarks that the following semester, he got a single - a room all to himself. He says this right before pushing the gnome out of the window and you can see (from the inside) it is indeed a different, smaller room than the one they were all sharing. But when viewed from outside, it can clearly be seen that he is in the same room from which he and Alex were throwing water balloons at Stuart. (Also director Andrew Fleming's cameo at the beginning of the movie of him yelling down to Eddy from a window is again that very same room.)