because overpairs are the nuts at 10NL and while he might slowplay them, hes very unlikely to slowplay them for 3 streets.

edit: Hand reading is just a comprehension test. Hes smacking you in the face with a big sign that says "I missed this flop". If you bet and he raises then hes lied to you at some point and you can decide whether he lied on the flop or he is lying now and you will also make a note for future hands that this guy is a liar. At the moment the story is coherent so believe it.