I have seen this behaviour took but I think it is coz u r either running the game in windowed or u are Alt tabbed out of the game PUBG counts taking your mouse to the other screen as Alt tabbing and doesn't minimize like other games ,
I have a gtx 1080 the card doesn't get over 85% but if I minimise it I reach upto 71c and 100% , I have gigabyte extreme card in other games at ultra maxed out doesn't cross 66C .but this 100% happens when game isn't in focus & full-screen .