I’ve never heard people say “cowboy chords” in a ukulele context, but amongst guitar players I’ve seen it used as a somewhat condescending description of players who use simple open chords and don’t play complex jazzy chords is solo up the neck. I don’t think it’s exclusively negative per se, just depends on how you use it. Plenty of incredible music has been made with simple “cowboy chords.”
I also notice this thing with guitar players where they think only complicated Polyphia level stuff is “real” playing. The reality is the general public doesn’t care much for insane shredding or complicated jazz chords and prefers the sound of simple, tastefully played guitar
Not hating on jazz or anything, but it reminds me of the old joke: pop is playing 4 chords to thousands of fans and jazz is playing thousands of chords to 4 fans