Cat scratch?

Hi there, so I have a cat that is dog-friendly, sort of like gluten friendly meals. He will hide and make himself inaccessible when need be but occasionally is curious. Once the dogs have been here for a few days, 99% of the time, we are all sleeping soundly in the same bed at night. But, if chased or pressed, he will stand his ground and swat and hiss. I recently had this during a drop off and the owner was cool with it, they knew I had a cat. After they left and we were getting settled in, I noticed the pooch was bleeding on his head a little! The cat got him! I feel really bad, but obviously that is a risk I am taking and the owner is taking too knowing I have cat that has their claws. What would you do? I feel like there are 3 options: message the owner now, tell the owner on pick up or let it ride. This is an indoor cat so he isn't exposed to much so I am not TOO worried about any infection or anything. I guess, let me know if I am making a mountain out of a molehill or should be worried a bit. I am a little new to Rover and want to make sure I am doing the right thing. Thanks for any advice, Cheers!