That detail was important to Rowan and finalized his decision. He realized the ways his enemies stayed ahead of him was by subterfuge and deception, if he does not know the true scale of their powers he would not be able to give a suitable response.
The same goes for his enemies as well, the less information they knew about him, the more pieces he would have to play with.
It was all the same to him in the end though, he would have to kill Erohim. Details about his second bloodline, his Angels, his rapid upgrades and his powers could have been laid bare before this fallen god, and even the ranting of Erohim may be part of a deeper disguise, and Rowan would never easily believe the words of beings that were thousands of years old, being duplicitous was something easily learnt at that age.
