I'll deviate a bit in saying that I do think sexual histories matter, but I qualify it by not really being mad or pissed about it.
Like people have said previously, the past is the past and can't be treated like some posthumous disrepectful dig at me or our relationship, but it is appropriate context as to where our relationship goes, assuming we stay together. First the lying is a red flag, it means you didnt just neglect to tell me something, you actively decieved me in order to control an aspect of the decisions about us that I get to make. I get to not want to be the sexual partner of someone that frequented gangbangs in her past. I don't get to make her feel bad about having done so, so obviously a precarious balance has to be met, but I dont have to accept it for my life going forward. And really why should I accept something now that you wouldn't let me accept earlier?
If the questions about said guys and said other sexual things were asked by OPs friend, then for whatever reason they were important to him and in the interests of an open and intimate relationship they deserved honest answers or at the very least an assertion of not wanting to talk about it all, which at least then puts onus back upon him if he wants to accept that or not.
The guy's problem probably carries an air of sexual jealousy, and sure he should attend to that in his own time and space, but the lying is on her and she deserves all of the disdain and mistrust as a result.