100% this...you should be able to decipher the autograph.....How tall was the guys grandpa?
At 15 he is already taller than the guy giving his autograph.
Smaller players back then tended to be wingers, but they usually stopped playing top level in their early 30's, as their game was all about pace.
The guy looks older than that, so may well be an Official.
If he has a copy of the autograph, can it be scanned and posted? Autographs back then tended not to be as scribbled and wild as they are now.
Inspector Clouseau Loyal.
I think the mystery has been solved, well done.