I'd say I have every right to retain personal pictures, taken in a public place. And yes, a hotel lobby is a public place.
If other people have issues regarding wanting to control photos, that is their problem. There is no inherent obligation on the public to comply, even if it is something a considerate person would do. So, if Friend asks, "Would you please delete those photos?" and Bystander says "No, thank you," Friend cannot do much about it.
I agree that running to photograph strangers minding their own business is quite rude. But rudeness does not entitle the entourage to use force (even very mild) to destroy the photographs.
And what if, theoretically, I was taking a picture of something else (the lovely fountain in the lobby, perhaps) for my own enjoyment, and Big Celebrity happened to blunder into the background? Would s/he be polite to demand that I destroy a photo that I took for my own pleasure, not because of his/her status as celebrity?