A person's name normally had some meaning or origin, such as Ning Que, Sangsang and Jun Mo. But of course there were always insignificant ones like Cui Hua and Er Ya.
Li Manman was called Li Manman because he was really slow. The way he spoke, the way he walked, or even the way he cultivated, it was simply slow.
He used seven years to achieve the State of No Doubts, much slower than his fellow students. But since then he speeded up. It only took him three months to reach See-Through. Then he achieved Knowing Destiny on the following evening.
That was Li Manman. Someone who started really slow, but proceeded the fastest. He walked slow but was the fastest in the world. Likewise, he never knew how to fight. He told that to Ye Su and everyone else. But no one would have believed it. When he started learning to fight and kill, he again surpassed everyone else in no time.