Right, so I had a talk with my dad about it, and he explained that they were just hugging for, like, 5+ seconds.  He has also said that, even though they both know that my dad is, like, madly in love with her, they haven't done anything line-crossing.  Not sure I trust him entirely, but I'll give him the benefit of the doubt on that.

He also explained that there are other things going on that I wouldn't have counted on.  It's still a bit of a harry situation, but, if my dad is to be trusted in this regard, no actual cheating has occurred.