@Marg11,
I would laugh it off and consider myself lucky that the guest did not complain to Airbnb, resulting in having to refund in full and then having your listing blocked until they investigate which could take weeks or more. I know it sounds unfair.
Personally, I block my calendar whenever any type of maintenance (other than lawn care or garbage pickup) might conflict with the guests' occupancy.
To answer your question: I believe Airbnb will deduct the $30 from your next incoming payment.
Keep smiling!
p.s. I'm curious, how did Airbnb know anything about the brief inconvenience, did you contact Airbnb yourself? Your guests have left very flattering reviews. Congratulations on being a wonderful Host.