9e7742db_ime_manipulation___Heroes_Wiki__Theory
[Citations] It was confirmed that when Hiro freezes time, it doesn't really stop, Hiro just slows it to a near halt. [Notes] + Logically, by accelerating time, Hiro would become very slow and effectively freeze. • If Hiro accelerates time for himself to the point where the entire world appears to be frozen, it's possible that he could do the opposite; slow down time for himself until he appears to be frozen to the rest of the world. [Theory] 
Hiro becomes frozen in time, because he (unwillingly) accelerates it very much.
Theory:Space-time manipulation - Heroes Wiki
Theory