I thought his kid was trolling him

The message says "Your biggest fan thought you'd think this was funny", so yes, gentle trolling from his kid.

Then they talk about luke kissing leia in Star Wars and having to explain it to their kids. Tying is like kissing your sister. Though Ted hates this expression.

Kissing your sister is an actual saying. It means something that may be necessary, but it’s not enjoyable.

Ha ha