Why on earth would they be doing a run-up on a crowded ramp while taxing out ?

From the timing of the radio calls on LiveATC.net the mishap occurred within a few minutes after arrival at the service center. I'm guessing single engine taxi on a tight ramp with loss of braking perhaps. I sure don't think anybody would use much above breakaway thrust on that crowded ramp.

The cell phone scenarios I mentioned seem less likely on the ramp but then, I have had coworkers with their heads buried in the phone while I'm turning into the blocks in a widebody. 'I already called clear right' is the reply if you question it these days. This multitasking texting is a generational thing I suppose.

Can't think of any reason, particularly as they were actually taxying in after landing at SAT.

And with passengers?

Being reported in some quarters that the incident was initiated by the aircraft clipping wings during taxi.

https://www.avweb.com/aviation-news/...ber+18%2C+2019