I don't see how this incident or guy is related to either MRA or the red pill.
At the end of a day, people from both sexes were killed.
Because a lot of what he said echoed stuff that regularly appears in those circles.
"I am a gentlemen, why don't women like me?" - Typical MRA nice-guy talk
"Women are all attracted to obnoxious brutes when they should be attracted to gentlemen like me" - Typical of MRA nice-guy talk and echoes RedPill alpha talk.
"I have not had sex because women have denied me it" - Typical of RedPill "women control access to sex" talk
"Women are too stupid to know what they want because they should clearly want me" - Typical RedPill talk about "weak minded" women
"My father gives this woman too much power, she must be good in bed" - Typical of both MRA and RedPill talk about women using sex to manipulate men
Granted, he took the absolute extreme measure, but a lot of what he said would have gone unchecked in those circles because it completely echoes their way of thinking.
As for the men he killed, his manifesto repeatedly talks about his hatred of men, and he hates them because he feels that they have had sex with women that he was entitled to have sex with. He doesn't hate them because they're men, he hates them because he hates the women that they've had sex with. His oldest friend was a virgin just as he was, and he was his oldest friend because he insulted anyone that he believed to have had sex, which inevitably was most of the people his age. There are countless tales of him hating people for kissing girls, having sex with them, and even just assuming that they'd done so. He targeted women because he felt that they had denied him sex he was entitled to. He then targeted the men that he assumed these women had had sex with. He said he was going to go to a sorority house and "slaughter" the women there, and he drove up that sorority house and shot at the women there, killing two of them.