Yep. It looks to me like the stairwell is awfully close to that door. A vantage point to attack from (rooms) and an alternate escape route (other than elevators). Though 32 floors is quite a ways up but he (they?) needed the elevation to attack as performed.
Floors 35-39 on that building are actually an entirely separate hotel, The Four Seasons, which has its own elevator banks but shares the same fire stairwell.
As to the “ISIS did it theory” The Four Seasons is half-owned by a Saudi prince and is a favorite place for Saudis to say in Vegas, and therefore must have a lot of muslims on staff.
Maybe the escape plan was up?