Did you take a reading? If you are around 1.030 - 1.040 (for a light to regular ABV beer) you should be fine, like said above, it could just be some break. If you give it a swirl, I bet it would go back into solution pretty easily. I'd think that if it were undissolved DME it would stick to the flask. And if I'm following you correctly, you had boiled in another container and transferred into the flask right? I doubt that it would be undissolved DME.
Keep your chin up and tell your roomy to watch WTF he's doing. I'm sure he wouldn't mind having some homebrew around the apartment.
RDWHAHB (just drop the second "H")
EDIT: Oh, I just thought - undissolved DME is usually kinda clumpy and sticky, so if you have a thin layer, I even more doubt that that is the issue - prolly break material