Skyy's play was called "Tent" and it was a slightly different play than the one KT scored on, but had a similar RPO set up with the same motion.
I think Kelce was supposed to be lined up on Skyy's side, and the motion would have Skyy come in to a stacked formation, but sprint back out.
Kelce was on the wrong side, so Mahomes initially thought KT had the motion, but put it together with a couple seconds left that the play was still good to go, so long as Skyy ran the motion.
__________________
.  .
|