That's correctHe seems to be doing 175 - 177 per battle. If that's true, it would have taken more than 100 battles to get to the current 17747. I think this is something new
This player was able to fight more battles as he unlocked many PvP regions these days and yes, by looking at his AP the number of trophies you guessed is quite accurate.
No bug here, just a really uncommon that happened for the very first time.