Maybe you are right . But its good to know that I had a full grown Oscar and a bunch of other Cichlids in that same tank when I got the catfish at 2 inches I put in that tank . A while later , when the catfish had grown to approx. 16 inches it attacked and killed my Oscar ( the biggest fish in the tank ) and left all the other Cichlids .
To prove your Theory , I guess we must switch things up , lets re-introduce the catfish now to the snakehead tank . now the snakehead is healthy , bigger and call the tank its home .
In my own opinion its because the Catfish attacks at night , The snakehead cant see anythin so takes a beatin and bumps into rocks and driftwood while it escapes . During the day , when the SH is weakend the catfish still attacks . It shows how persistent these Catfish are , since it wasn't deterred no matter how much the snakehead bites or fought back .