Are there actual glitch "artists" or does this stuff just kind of happen?
that honestly depends. there are a lot of glitch “curators” out there, finding stuff that looks glitchy, or waiting for genuine faults in systems.
most of us create the glitches, though. there are many devices out there for creating visual interference in video footage (shoutout to @tachyonsplus and @glitchartdotcom), but there are other, more primitive methods of crafting glitch art.
my setup, for the longest time, was insanely primitive: a source footage machine, a frayed wire, and a vcr. the simple act of interrupting the signal between the source and the recording medium would create interesting effects on the tape.
manipulating that frayed wire became sort of like playing a one-stringed instrument. the angle, the speed, and the direction of the interruption all create different effects.
now, the setup has advanced a bit: there are more machines, but the aim is the same: finding the beauty in the destruction of the analog signal.
if you’re genuinely interested, i would start here for a primer of glitch art: http://kernelmag.dailydot.com/issue-sections/features-issue-sections/12265/glitch-art-history/