How did Shubman Gill get dismissed if the bails didn't fall in Hawk-Eye?

Gill was initially given out by the umpire. The UDRS indicates the expected path of the ball toward the wicket, and if this is within a margin of error, the decision is too close for it to make.

In this case, the decision is left for the on-field umpire, and usually unchanged, as shown by the text

Wicket
Umpire's Call