Surely, there would be physical evidence of her biting his thumb? Its not 'normal' to bite someones face, and i don't see how biting her lip when his thumb was in her mouth would make her mouth release his thumb, it makes no sense whatsoever. A natural defense would be to perhaps hit her to get her off, not clamp your own mouth around something clamping your thumb.
I cannot believe the social media bandwagon who have supported him, saying she should also be punished, psychological abuse is terrible but it does not in any way excuse what he has done. That was a vile act that would have taken a split second of thought atleast. If she genuinely bit his thumb, it would have been recorded by the police and it will come to light during the trial and his sentence will be lighter as he can put it down to self defence. I'm not holding my breath for that though.