The flyer for this mentions Loser (Beck's band with Steve Hanft) and Skunkhead (apparently a different metal band that might have had Beck in it too).
However, we have a second flyer for a different show at a different location in LA that says Beck opened for Possum Dixon on the same night.
It seems possible: the Possum Dixon gig at the Jabberjaw was at 9pm (and Beck was probably first). The Loser/Skunkhead show was at 11pm. So he easily could have performed, zipped up the road to Al's Bar, and played again.