In trying to return a spike, B1 attempts an overhead pass, but does not accomplish the perfect finger tip pass. There is a "thud" sound and there is contact with the palms of the hands, but I can not see prolonged contact. Is this a legal hit?

You answered your own question. If you didn't see prolonged contact, it wasn't illegal.

Remember that "ugly" and "sounds funny" are not necessarily illegal.

This sounds a high dig. Perfectly legal, high level play.

As has been noted already, if you didn't see prolonged contact, you can't call it. It is not illegal for the ball to contact the palms, and it is not illegal for the ball to sound any particular way.