Using Minor Illusion to create a 5x5' cube of stone, one of my players who was a 6'4" ranger claimed it gave him three quarters cover and that he was shooting over it. I was okay with that. But after an Orc shot an arrow at him, and missed, I wanted to say that it broke the illusion by hitting his illusory stone and passing through - but he argued that it wasn't "physical interaction" as the Orc didn't use an action to target the stone.
Is it, or isn't it? Does the way the spell is written require walking up to the illusion and touching it/poking it with a blade, or targeting the stone purposefully with ranged attack?
Clarification: I guess what I'm asking is, can the illusion be broken unintentionally, or does it require an action?