Sounds like he was just playing his part for switch day; unless he does that on normal days too. Teens will be teens; let them find their place; the more you try to push them, the more they will resist you so let this go and save your battles for serious stuff; life will be a lot smoother with them.
Amen.
From what you've written, there's no problem so far.
Your daughter doesn't like girlie stuff.
So what?
Your son got into the role he was expected to play.
So what?
If they start acting like homosexuals - no dates with the opposite sex, looking at homosexual porn, etc. - then you can get worried.
Your son sounds like he was only getting in touch with his feminine side for the event and sounds pretty normal to me.
As for your daughter, well she is probably just another clone schoolgirl who think that they look nice in trousers.
I see schoolgirls pass my house everyday on their way to and from school and more than 50% look dreadful in their Maroon trousers, unlike the remainder who look delightful in skirts.
When she realises that only a very small number of males like girls in trousers she will take to wearing girls clothes, unless of course (and I hope not) nature has messed up and she does not like males.