Hi Joel,
I'll add the answer here as well as the email I've sent you, because it's relevant to people importing backups for restoration in the wordpress.org version, as well as migrating via the add-on.
The file you're importing ends in:
db (1).gz
That ' (1)' must have come in through saving two copies of the file on your computer. But it causes UpdraftPlus not to recognise the file as a database - it is looking for the db.gz ending. So, rename the file and then try again and it should work.
David