Hah, pretty cool that he’s into rock. I also began my musical adventure playing rock/metal on an electric guitar. 
Really good effort for 10 years old. I think that guitar is even harder than piano at that age because of how the strings can slip and slide without enough pressure from larger/stronger hands. Can imagine how happy he’ll have been recording it yeah. 
Hope your son keeps on practicing many hours, there’s nothing like playing/writing music. 