Ugh, scientists. Hiyoshi couldn't care less about Inui's work being set back, but the fact that Inui was holding his ground despite what Hiyoshi knew was not an insignificant amount of pain, meant that this was clearly important to Inui and he was likely to put up a fight if he didn't get his way. In this situation, it would be faster to let him have his way and put the flask down... if he could trust Inui to do that and only that.

"I am going to let you go so you can put the flask down safely, and then we're both going to evacuate without any other delays. Understood?" With that, Hiyoshi let go and stepped back. If Inui didn't comply after this, he'd just have to knock him out.