Ethernet speeds historically were measured in 10/100. In my past life I worked for an a small rural isp. And part of my learning I was taught that cat5 was 8 strands of wire, or 4 twisted pairs. I got very familiar with crimping patch cables. If one strand were cut a network card would negotiate down to its lowest speed and still work at 10mbps. Operating on 4 wire or two pairs. It’s possible with those numbers you had a bad connection, or a broken strand in the cable and it auto negotiated down to 10mbps. To this day I still crimp my own cables, and I own a cheap cable tester to make sure the crimps and cables are good.