I think they mean that Chris could claim that someone running up to them and waving something in their faces is reasonable grounds for self defense.
If that argument is successful then using pepper spray is potentially lawful.
It’s not cut and dry, but it’s certainly more of a justification than just pulling out a spray and spraying someone who took a photo from a few meters away without asking.
Virginia basically says you do not have a right to privacy if you're out in public. If Chris and Flutter are walking down the street, and someone comes up and takes their picture, doesn't initiate any kind of contact, there's nothing either could do about it. If it's in a mall, then that's up to the mall if they want to kick that person out.
Chris "gets scared" and pepper sprays someone will not go over well for him. He already has a ding on his background from the GameStop incident, which will come up with a casual background check, which will not help him at all. Besides, what's he going to say?
Police: "So what happened?"
Chris, completely out of breath, sweating, stuttering "This this troll ran up and took my picture and waved something in my f f face and I sprayed him!"
Police: "They hit you with something?"
Chris, flustered and breathing heavily, "No they took my picture! I was scared because they waved something in my face!"
Police: "Can you do me a favor? Turn around and put your hands on top of your head"
"Being scared" does not allow anyone in Virginia, or most states, to assault someone. Doesn't matter if they're evil trolls or whatever. It sure didn't help Chris not get arrested after the GameStop and it sure won't stop him getting arrested if he does it again.
One bonus thing is, it appears Flutter is a foreign national. If she has anything to do with a potential Chris assault, the laws are very, very different, and she'll be spending some time in a jail cell potentially for a ICE hearing, which may result in a ban coming to the US.