I must say I am very surprised (based on what you’ve told us). Have a look at the guidelines:
https://www.sentencingcouncil.org.uk/offences/magistrates-court/item/inflicting-grievous-bodily-harm-unlawful-wounding/
Whilst it’s true that an offence considered to be in Category 3 of seriousness (the least serious) could be deemed suitable for the Crown Court (because the guidance goes up to 51 weeks custody which is beyond the Magistrates’ powers), it would be unusual. As you can also see, to be seen as a Category 2 or 1 offence serious injury must normally be present. The Magistrates must have believed the injuries to be more serious than I imagined.
What you must bear in mind is that the Magistrates believed the offence warrants a sentence beyond their sentencing powers (which is 26 weeks custody). There is no guarantee a judge will see it that way and in any event if a custodial sentence is imposed a suspended sentence may be a strong likelihood in view of the fact he has not been in trouble for some time.