Thing is, I kind of understand what he meant. From Bob's perspective, he believed Lindsay had led him to believe they were friends, and the sudden reversal took him completely by surprise. I think by "gaslit" he meant that Lindsay had intentionally (or maybe unintentionally, hence "borderline") given him the impression she enjoyed his company (and maybe his affections, someday!), and the tactical nuke blindsided him.
The problem, of course, is that you would have to be an absolute moron to think Lindsay had led him on in any way, and not just because of the softblocking. She never acknowledged him, retweeted him, or sent potential new viewers his way. She barely engaged with him at all. The only way the gaslighting accusation made sense was if she was communicating with him privately, and I'm sure if she had been Bob would have said something about it after she blasted him.
It really demonstrates how incredibly delusional he is.