Yes, that would be a strange thing to say, and unless they also happen to be boaters, most mechanics probably have no idea what side “starboard” is, and maybe not even “aft”, so it won’t even be useful information to them, which actually makes it quite frustrating. Similar to someone coming in with a vague and incomprehensible complaint that there car is making “a noise” and they want it fixed, but they can’t explain in any useful way what the noise is, where it’s coming from, when it happens.

Just to be clear, the correct and accepted terminology options are “rear passenger side”, or “right rear”.