The part of sending money to the scammers addy would make sense as a test, but both were made on the same minute, and AFAIK blocks aren't mined that fast yet
In order for the test to succeed, they would have needed at least a few minutes, for the transaction to receive confirmations and to appear in the thief's wallet
Not at all. No confirmations were needed and only a couple of seconds were needed to confirm the test transaction. Also, no block explorers were required.
If the thief opens his wallet and gives OP an address, and OP sends 10,000 sats to that address, the thief's wallet will show the incoming transaction within two or three seconds. You can test this yourself when you pay for something using a payment processor, which detects your transaction seconds after you hit send. You can even test this yourself by opening two Electrum wallets and sending coins between them. As soon as the transaction is broadcast, it is relayed across the network within a few seconds. Seeing the transaction show up in the thief's wallet, even with zero confirmations, is enough to confirm the address is correct. OP can simply click on the same address, click "max" or "send all", and click broadcast. The whole thing could be done in 10 seconds.