Just looked at the script:
XANDER:
I didn't know what was gonna happen!
I just heard, you know, revelries and
song and... I wanted to be sure we'd
work out. Get a happy ending.
Never saw this particular episode in original tone since the songs are subbed in the German version. The speech parts are, however, synchronized and sometimes a bit different in context. Did he really say "revelries" in the sense of big orgies? At least that's my dictionary comes up with as a translation. 😀
However, it implies that he knew about the singing and dancing. At this point, he had learned the dangers of magic and summoning, that there are always consequences. He should know better but I can see your point Mr Trick. Well, since I don't like the music I have to rely on the rest, which is the plot and its consistency.