I wouldn't necessarily say that shortening it to 5" would preclude it from being a competition gun. Could be that the owner just liked the balance better with 5", or maybe there were some matches that required 5"? or maybe when this work was done the owner just thought that there might be some matches that required, or would require in the future a 5"?

Reading through all the old competition shooter's books, and what I can find in old magazines and such, it does seem that rules would change from time to time. I can see a fellow who is having the sights done for a match maybe trying to get ahead of the game and putting the barrel down to the same length as the 1917s... just in case.