How to Reduce Mysql Size After Dropping Table
You seem to have leftover some temporary file of the ARCHIVE engine: https://dev.mysql.com/doc/refman/8.0/en/archive-storage-engine.html

This engine is barely supported, and I would not be surprised that is has bugs. Assuming there is no .arz file, and that no client is accesing it, it should be safe to drop. One recommendation I always follow is to rename or backup any db-related file before removing it. That will give you an extra guarantee in the worst case possible.

As an extra comment- avoid archive engine at all costs- if you need a compressed table you can use InnoDB, TokuDB or RocksDB.