I could see it happening as a fluke. AFAIK clams don't have any kind of taste for fish and if it happened before it was probably because the fish swam right over the clam close enough to get caught in the mantle. Clams will close up quickly from the slightest change in light. Happens to mine all the time if I even wave my hand next to the light where I don't really see an noticeable change in the light intensity, but the clam picks it up and realizes there is a change and possible threat above. Fish got too close swimming over it, clam shuts, oops. I think if this ever happened it is not because the clam wanted to eat or even kill the fish. They are filter feeders.