Kelgil at 12 weeks your uterus is just or about to pop out of your pelvis. There is a ridge that can be felt when this happens and it's the top of the uterus - it's called the fundus. I am sure this is what he meant. He "thought" he could feel the fundus.
By 13 weeks you will certainly be able to feel it if you use your hands to press down just above your pubis...

If you are at all concerned you can ask for a 12 week u/s for reassurance...