I'm wondering if it was a partial pinch flat from hitting whatever it was you ran over. I was riding gravel one evening, racing home as fast as I could because I was losing daylight. Hit something hard that I didn't see as I was going down a hill, but I could hear the air hissing out of the tube. Since it was getting dark and I didn't want to ride 10 miles of gravel at night even with a headlight, I called my wife to pick me up.

Later at home when I repaired the tube, I found I had not one but four punctures from running over whatever it was, a pair of pinch holes. That happened with 700x25 tires, now I run 28's. But if I ride gravel, now I've got a dedicated gravel bike with big 26x2.00" tires.