There are alot of indications that he was involved in several parts of the 'manosphere'. Like this graph he made:

https://www.google.ca/search?q=elliot+rodger+graph&biw=1440&bih=763&tbm=isch&imgil=UITvf76mQWlBNM%253A%253Bhttps%253A%252F%252Fencrypted-tbn3.gstatic.com%252Fimages%253Fq%253Dtbn%253AANd9GcTFRQG1qCIRq5BfWrtpfcShFyNYWCdhHszVwRVAH4JWJ7nr-79Y%253B615%253B409%253B5Pn6XcAK_ZkiNM%253Bhttp%25253A%25252F%25252Fwww.mirror.co.uk%25252Fnews%25252Fworld-news%25252Fcalifornia-shooting-three-bodies-removed-3603730&source=iu&usg=__GTchg1uoUfjNSDthcmUIqGHzFW4%3D&sa=X&ei=mb2GU6SaLKjK8wG-0IDwCg&ved=0CDIQ9QEwAg#facrc=_&imgrc=UITvf76mQWlBNM%253A%3B5Pn6XcAK_ZkiNM%3Bhttp%253A%252F%252Fi2.mirror.co.uk%252Fincoming%252Farticle3602460.ece%252Falternates%252Fs615%252FElliot-Rodger.jpg%3Bhttp%253A%252F%252Fwww.mirror.co.uk%252Fnews%252Fworld-news%252Fcalifornia-shooting-three-bodies-removed-3603730%3B615%3B409

The first two graphs are a very common topic in manosphere sites. The idea that basically 5% of men have sex with all the women and the other 95% of men don't have sex. Of course, there's nothing intrinsically sexist about this contention. For some, it would be merely a sociological observation. For Rodgers....it was justification for murder and hate.

But it's not a coincidence that he's espousing this view and he didn't formulate it himself. He got that from the manosphere.