Grounding either works as the multiswitch is a grounding block. However, as you say he still should put a grounding block outside near his grounding rod. Ground the signal before it enters the house.
Even better is just put the SW64 where he'd put the ground blocks - saves an extra dozen F-connectors. The fewer the connectors, the better!
Even if it's a bit of a hassle to run the power to the SW64 he's still ahead.
On the other hand, if he "can't" put stuff outside, and is thinking he's OK in grounding AFTER it enters the house, well, that's just dangerous as we all know.