Yes, without getting into politics...
This is probably not the first time an international Air BnB guest has asked to cancel for safety reasons. It is a new and unsettling varaible for hosts and guests who've never faced this concern before, especially in such a previouslywelcoming free-flowing global market.
Humanitarian compassion comes to mind initially. The guest is already facing contractual restrictions by Air BnB cancellation policies (which are far less of a concern than the stated reasons for cancellation). Air BnB will handle that as they will, and likely check to see if this guest has a habit of cancellations, and you have the option of declining should this guest ask to stay with you again.
It sounds like you have a thriving business and the dates freed up will be booked...perhaps at an even higher rate for those last minute planners lol...
You can transform this into a "win-win" with kindness and optimism, which is a perspective that could serve well in many arenas...