You are correct. From the background notes [1] on the band's page:

"It is not all one speed, but each section is at a constant rate, meaning that time does not “ramp” (accelerate or decelerate). We just toggle from one speed to another. When the guitars explode, we are 200x slower than reality (6,000 frames per second), but Tim and Andy’s short bursts of lip sync (Tim twice and Andy once) are only 3x slower than real life (90 frames per second). The watermelons are around 150x, and the spray paint cans are a little over 60x."

[1] http://okgo.net/2016/11/23/background-notes-and-full-credits...

I doubt it. In the article someone else linked they said all the events were pretty tightly coordinated. I don't want to take the time to actually nerd out on the math, but it seems like there'd be one ratio you'd apply to everything. Like if the song's 124bpm at 60fps (2.066..7beats per frame), you'd want to multiple all that by 100 if you're shooting at 6000fps, so like 206.66..7 beats per frame. THen you can run the video back in super slow mo (60 fps again) and get the real 124bpm deal?