Inevitably, a fair amount of anthropomorphization is taking place, on the part of the spectators.  Kaufman's guide to Mammals of North America says, "Adults tend to forage alone but often rest in groups, called 'rafts.'"  There is a photograph of such a raft, with around fifteen otters in more or less close contact, and another of a pair of otters side by side, just like the pair in the video.  Apparently there is safety in numbers and in togetherness, and the linking of the paws is done so that they do not drift apart.  That is one of the most interesting details in the video, in fact, that after they momentarily were separated and started drifting apart, the one went after the other and linked paws again.

I suppose it is not impossible that sea otters are socially cohesive, and their groups are something like packs.  But I do not know enough about them.  Do they chase away strange otters who try to join them?  Or do they accept strange otters easily?

Chickens deserve our true friendship! So do fish! So do other sentient beings! Let us learn to be kind.