So I took on Whitney, the normal type gym leader in a rematch battle. Using my Mismagius, I accidentally used shadow ball on her Delcatty which of course did nothing.

Here's where things got weird: Delcatty, used assist, used thunderbolt, icebeam and the like- none of which affected Mismagius. Does assist make the move normal type or was it because of my shadow ball?

Delcatty's ability is Normalize, which makes any moves it uses be treated as Normal-type.
It's no glitch.