Right, "regular coworker" lol. That's the same energy as calling your best friend "someone I know" or saying your favorite food is "okay I guess." We're all out here acting like we don't care about anything. Next we'll be saying our own birthday is just a regular Tuesday.
Honestly I see this all the time, people really play down their relationships by calling them "regular." Like they'll be genuinely close with someone but act like the bond isn't deep. It's a whole thing to make everything seem super casual.