This isn't necessarily true (and is very dependent on what your password was) - they could have iterated through lists of common passwords w/ special characters, hashed them, and compared them to their DB, forcing a pw reset for everyone that had a match.
edit - just want to state that if they disallow special characters it really is a terrible policy, my point is just that resetting your password isn't proof they are stored in plaintext
edit - just want to state that if they disallow special characters it really is a terrible policy, my point is just that resetting your password isn't proof they are stored in plaintext