[GabrieliosP]

Spoiler for The probable answers:

Irie most probably knows that Miyo was the one to order the Yamainu to do it (or he might suspect that the order came from Tokyo), and if he suspects Miyo, he probably thinks she just went a little too far to prevent the stop of Rika's tests (it's not like he can tell the truth to anyone outside the clinic, Yamainu or Tokyo without endangering himself).

Also, it's not like Rika's parents would tell people that their daughter was being tested frequently at a clinic. Irie or the Yamainu probably covered her visits the same way they hide the truth from Satoko: not lying about it happening, but lying about the reasons.