As others have said, I believe that Trask had become hostile to the rest of the Collins at this point, especially Quentin, even more so after learning about what transpired between Barnabas and his father back in 1795. He didn't want to believe he could have been wrong about Quentin.
I mean, his dad, the originial Trask was pretty much the same way. Nothing convinced him that anyone other than Vicki could have been the witch until Barnabas showed him up on it.