Of course he would not pursue it. There is this dragon that said to be bane of kingdoms and here in front of him someone who he suspect to have defeated it. This is not skyrim and he is not a bandit.
There are 2 reasons why he faces this issue:
1. He is the MC and hence a living calamity magnet.
2. He raised the flag himself by especially asking if there were no strange occurances in that place.
The MC hails from Japan so he should obviously know about the effects of being a transported/summoned/reincarnated person and also about the issue of raising flags.
Yet he still did not account for either of it.
where does his negative Mana come from? Does he tap into God himself to split the difference ? And what happens when people drink mana potion's with too much mana? Do they explode are they posioned are they drugged up