Didn't see it.
Sounds to me like BU assumed a strike because BR ran and had to call something. If no other runners, easy enough to reverse if umpires agreed later it was not a swing. With other runners, especially if there were 2 outs, could be a mess.
Probably smart of BR to run just in case, but should have sooner. Hopefully, the umpires would have been objective enough not to use that to determine if it was a swing.