Probably a school project where the two girls were forced to be on Mr. Beard n' Hat team. His enthusiasm to pull of this idea persuaded the girls, with the conjectural promise they might become more popular.
Granted, a lot of things sound better on marimba, but when a couple people on marimba blow your 'prog' band out of the water it's time to rethink the ol' career choice.
To be fair, the bearded and hatted gentleman is playing the wooden box or caja, a latin american percussive instrument. Don't make me pull out the race card, because I'll do it, gringo.