Constables are not cops, in general. IDK how exactly it works in Texas and it looks like it's actually more similar than it usually is, but as a general rule in practice, constables are sort of the "civil matter" version of police (who are chiefly for criminal matters) -- they serve evictions and summonses, child support warrants, traffic detail like in this case, that kind of thing.

Best I can do is paid administrative leave

The Best I can do is charge the driver with a misdemeanor instead.

Fuck cops and (most) DA's while we're at it.