@Imogen23 I agree with Roberta, that it doesn't really sound like this was an emergency, unless there was water flooding all over the floor. If it was just a matter of your clothes being in the broken machine, you could have arranged to go over and retrieve the clothes at the guest's convenience, and taken them to the laundromat. If it was a matter of the washing machine being one of the amenities for the guest, you could have offered him a small refund because it wasn't working. It wasn't really the guest's affair to deal with the tradesman, nor should a guest be expected to feel okay about some stranger entering when he isn't there.
A this point, I'd send the guest a message, sincerely apologizing for the inconvenience you caused him. You'll just have to live with the review he leaves. There's really no point in worrying about what someone might say in their review- sometimes hosts have been anticipating a bad review and were surprised when they got a good one, or the guest didn't even bother to leave one..