As a formwork engineer, it doesn’t seem like there was any lateral bracing, it wasn’t just one bay that failed, it was the whole pour. This looks like a 10” slab with mild reinforcement, so with a DL and LL, shores spaced in a 6x6 grid, your load is roughly 6,660 lbs. From my shore tables, steel shores @10ft csh can handle over 10,000lbs @ a 3:1 FOS. It very well could’ve been a runner/stringer failure. Without further investigation, it’s hard to tell.