Musicians - in this case bass players, but it certainly applies to other instrumentalists - generally fall into two categories. The cats that get called back for more gigs, and those that don't. You pretty much just described the second one. To me, the best judge of my playing is whether or not I get asked back. I always try to put myself in that first line...sometimes it's long, other times it can be much shorter.
So, I know this sounds a bit Darwinian, but I tend to keep my mouth shut and potentially land the gig for myself.
If, however, the fellow musician is a friend and has invited feedback, I'll provide it...hoping for the same in return. I play a bit too busily at times, and it's nice to get objective information from someone with a good set of ears. In your case above, I'd guess that the first fellow is grateful and has landed many more gigs as a result.
