I work in homicide, so our jobs mostly really end in life sentences, but everything you need to know is here:
https://www.sentencingcouncil.org.uk/offences/magistrates-court/item/assault-occasioning-actual-bodily-harm-racially-religiously-aggravated-abh/
He might be right, it might be in the lesser category, but I have absolutely no idea of the circumstances of the case. Sadly I know just how much you’ve got to do to get a term of imprisonment, so I’d think it’d be unlikely he’ll end up with custodial.