Is it possible that this was a transaction in a block they mined themselves? instead of publishing the transaction to the pool for any miner to include, if they kept it private and only put it in a block they mined, they keep the fee right? I don't know why they would do this, just thinking.
No the account used to publish the transaction can't not mint it. Mining delegators are chosen at random for ethereum. You will need to look up "Proof of Stake" to understand how the mining process work for ETH.
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