Sounds to me like Mr Evans went down on what statisticians in times of confusion call a guesstimate
Does she remember consenting?
Were there 3rd party witnesses?
Did she say, "Yeah I likely would have consented to sex with 1 guy, but no way would I ever consent to a second joining in - especially since I had met him earlier"
etc etc:
Without seeing the court transcripts there's no way to know. Or maybe she said she didn't consent to either but there was enough evidence to cloud the issue and make a conviction unlikely. Maybe the jury liked one bloke more than the other. Maybe... etc:
As I say, consent is the hazzy area legally. Drunk people can consent and not remember it - there is still ongoing battles over that being true consent though.
If drunk people 100% could not consent, then how many relationships are based on rape? Or a woman sexually assaulting a man?