Well, Magos' characters have no possible way to know if Toshi did or did not hear anything Tom said. Hell, they weren't even in the room at the time, so Magos has precisely zero IC reason to be involved in this.
The fact is, if Toshi didn't hear it then he didn't hear it, full stop. That isn't a matter of him being "thick", that's a matter of him not hearing it. Even the smartest person in the world still can't act on information they don't have.
Admittedly, there are plenty of other reasons why Toshi should have thought twice before healing the guy, but none of them are anything like as blatant as "he heard what Tom said".