I've never seen anything about hyaena specialising in man-eating after having tasted human flesh, but I've seen lots about hyaena taking human flesh.
In rural, wild Africa it is not too uncommon to see people with disfigured faces, or limping, with severe wounds to the feet or lower legs. If you were to ask the question is invariably mphisi!
They don't necessarily go for the human, but they take the opportunity to get hold of a piece of meat. If that piece still happens to be attached to a human, that's too bad, they take it anyway.
They may be afraid of humans like all wild animals, but when it is dark and everything is quiet they sneak into camp, and grab whatever they can. Especially in the later parts of the night when the fires have burnt down, is the chances bigger that they'll try than when it is still early and the fires are burning high. But also, when they've become too accustomed to humans, and some of the fear has gone (there's a big difference between 1800's and 1900's meetings with humans, who would have bene mostly hunters that shoot, and current humans, that are campers and don't even have firearms, let alone the will or inclination to shoot!) they may be bolder and actualy come in earlier. Why not? Nothing to be afraid of. But they're also clever enough to know that they shouldn't be doing that, so it is a hit-and-run type situation.
Over the years many a hunter/camper/explorer have awoke to find that a hyaena had been in camp, and took something, or more than one something. Knives with rawhide handles chewed the handle off. Old-style rawhide thong camp chairs. Leather boots. Leather hats. Skins. And of course meat, be it fresh, biltong, whatever.
As for groups? Yes, the hyaena is a group animal, but it is not uncommon to see them off ranging alone, or in group of two/three. And the prey tackeld when they hunt will also depend on the group size. Small groups = small prey. Big groups, anything up to buffalo is possible.
Hunter, nature lover, conservationist.
I believe that for man to survive, we must work with nature rather than against her. We need the land; the land doesn't need us. Too many people have lost sight of this fact. - Bruce Truter