I have no idea if what "roll" means to me is what it meant to the audience member in the OP, but I thought the remark made sense. It's about the microdynamics and micro-phrasing that good bass players have intuitively in their hands. It's hitting the note with just the right degree of attack, at just the right time and in just the right place on the strings, and then letting up on it at just the right moment. It's setting up your fingering as you go so that you always have the next note set up to hit cleanly. It's doing all these things so smoothly and surely that it doesn't sound like you're sweating those details, but just feeling the line and the way it moves the music forward. And when you do all these things, it makes the listener move their body in a relaxed, rolling kind of way, hence the word. I think it comes out best in grooves with a swing or shuffle feel, though it could also be a quality of a straight-8 beat with a player who has a bit of inherent swing in their touch.
To me the ultimate example of "roll" in a bass part on a pop record would be Leland Sklar's magisterial track on JT's "How Sweet It Is".