Awesome, thanks for the vouch.
Seems like he inserted it Antpool based on the tx he accelerated. Not sure if Antpool was offering this service and OP is just a reseller but still, I think it's legit. Though $12 seems a bit steep, but this is some kind of cure if you happen to make a mistake when putting fees. Like in real life, cures are expensive than prevention.

IIRC AntPool used to offer an acceleration service to miners on their pool, but stopped. My guess is that OP pushes the transaction through BTC.com's accelerator, and basically is using this to convert money from a credit card into Bitcoin. BTC.com is owned by Bitmain, which owns AntPool, so that is the most likely answer in my opinion.
I just also realized this. Since I did a research on how this could have been done without real connections with antpool and other big miners. BTC.com has really steep charges on per transaction, much higher that what OP is charging. I tried to check a transaction with 250sat/b, it cost around $35 to accelerate.
I guess, OP might be using this, no guarantee what it is though. He might be or not, using carded credit cards acquired fraudulently and using it to pay BTC.com. But, we'll never know unless someone has access to BTC.com and can confirm that the transaction I had was pushed using their service.