Summary:

The elevator was full. Too many people were packed in like sardines, and their suitcases just made the squeeze even more unbearable. JJ didn’t feel the need to add to it. He was six-foot-five and as wide as a brick wall. He didn’t want to be packed in there any more than they wanted to share the space with him.

He decided to take the stairs.

OR

JJ takes the stairs at the exact wrong time and overhears The Phone Call™️ from Moscow. He, in canon typical fashion, does not take this well.
(Fuck AI)