Hope it's his own;)
Yes, otherwise it would be "Han har en stor tunge i hans mund".
Not necessarily. :-) If it is the tongue of someone else, hehe.
Does this have some special meaning in danish culture?
No, it's just another 'The crab doesn't like group work' type of sentence ;)
Probably Gene Simmons ;)
Does this have some other meaning, or is it literal?
It isn't a saying or anything, so I assume it is meant literally.