I could be mistaken, but this appears to be the same group that was performing during the Marathon a few weeks ago, immediately after exiting Dinorama, around mile 17.
When I ran by, they were singing "Magic Happens," the theme song from the parade at DL, which stood out to me for a few reasons:
- Music from the parks is rarely performed outside of its original setting
- The parade only ran for 2 weeks on the opposite side of the country, so it was unlikely many runners would recognize the song
- It was bound to fuel baseless rumors about the parade coming to WDW (it's not)
- The group must have been a Disney group, but didn't appear to be one that I recognized (like Voices of Liberty)
Outside groups (high school marching bands, DJs, kite teams, etc.) often perform at runDisney events, so it wouldn't have been unusual for a non-Disney group to perform in this location. Yet this unknown Disney group showed up instead. And with their matching white pants and coordinating jewel-tone jackets, they seem to have been somehow related to the 50th, though the connection was far from clear when running past.
Due to their location immediately after leaving the onstage area of the park and somewhat obscured by containers, there don't seem to be many photos or videos showing them during the race. Even in bioreconstruct's aerial photos of the course through DAK have them just out of frame. I found a few videos where they can be heard singing pop songs like Uptown Funk, and they can be seen around 28:20 in the video below singing The Lion Sleeps Tonight (which I suppose fits the location). In general, there doesn't seem to be a particular theme to the types of songs they performed.
Oddly, for a one-off event where they were located backstage next to literal dumpsters and storage containers, they had matching outfits that clearly indicated they were a professional music group. Yet for (presumably) regular performances onstage, they look like they're just wearing whatever clothes they had on that day, and could be random guests who started singing. The group already has costumes; why aren't they wearing them?
The performers seem to be quite good. It's the higher level decisions about the group that don't make sense, especially in a time where all forms of live entertainment in WDW are so limited.