Years ago I set a goal for myself to learn and review meseches Makkos 101 and times. I never made it to 101 (I think I stopped at about 50). The first time I learned the it, it took about 5 weeks. After that, I reviewed it about 10 times at one week per review (about 3 1/2 blatt a day). Eventually, I got to the point were I could work through the whole mesechta in about 3 hours. It isn’t inconceivable that this guy really was learning, he could have a unique mind that thinks rapidly in this way (nothing to do with raw intelligence necessarily), or he may have learned that gemarah many, many times.
Be dan l’kaf zechus, and don’t do as he was doing if you know that for you its not real learning.