Cache store flush is not going to cause any problems with a restore. Other way around, restoring a database will flush the caches. It's not an error, just SQL notifying you that some operation (like a restore) required the caches to be cleared.

If the database is still in the restoring state, good chance that whoever restored it restored WITH NORECOVERY. That means restore the DB and leave it in the restoring state.

Maybe ask whoever restored the DB what command they ran.