they went "double time" and into charlston. Many LindyHop dancers have huge problems dancing to slower or slow-mid range of music, but can go mid-fast to fast (which is more typical in swing). With slow songs a lot of lindy hop dancers will go into mixed blues dancing if they know it, but many cant do slow tripple steps and really roll thru their feet. At least "normal, I sometimes go social dancing"-dancers. Slow dancing requires more technique than one might think - rolling count!

No wonder, she's mainly a Lindy Hop pro

Out of nowhere he tells her to halt in the middle of her count and she stops before reaching the next step. They're cheering her follow reaction time.

And because he switches from Lindy to West Coast Swing in the middle of the song and it works!