Or, could it be the genuine excitement of the SpaceX team that was getting captured in the stream? As the commentators mentioned, the team were able to read the telemetry data even when the onboard camera became dysfunctional. And, I'm sure that lots of viewers were also cheering for the flap.

The on-site audience might have access to milestones the rest of us don't see, hence the "for no apparent reason" cheers.

I'm delighted by the cheers. They're doing amazing things, and I'm pleased by their passion.