TNA used to have a rule where you could lose a title on DQ. It was something that was implimented at the start and done once early on when Jerry Lynn & Amazing Red lost the Tag Titles to Triple xXx and forgotten about until Abyss won the title from Sting.

However there was another title match that ended on DQ that wasn't counted. And it wasn't a mistake either. It was Sting vs Jarrett during the whole "let's try to get Hogan in TNA" bullshit with Jimmy Hart.
By all means Sting should have won the title but no one remembered the rule.