A lot of things factor in to what works best including individual variations (eg tolerance for cold, how hot you run) and specific weather factors beyond just temperature (rain, humidity, altitude, wind, cycling speed, sun vs shade, etc.).
Play around a bit and experiment. Eg, next time go ride for 30 mins with no bib shorts and just the thermal cycling pants. Or replace the pants with leg/knee warmers. That’ll test the hypothesis @HLaB proposed.
Also, how cold was cold? A little uncomfortable, or stop-the-ride cold? Usually when riding in winter, I’m rarely fully comfortable for the entire ride - there’s usually something that’s not ideal. But once I acknowledge that reality, it makes it easier to just get on with the ride.