My default answer to anything regarding “could the IRS do xyz?” is always yes.
You could spend the next several years worrying, or you could call. Keep in mind there is a chance that when you call, the person will be able to explain why, in your particular situation, the IRS is right and H&R Block’s program was wrong. Then you won’t have to worry. I actually suspect this is the most likely scenario.
Your refund is very much a Schrodinger’s cat right now. If you call, you could be informing them they are wrong and lose your refund. But you’ll never have to worry. (Dead cat) Or you could find out you were wrong, get your refund, and never have to worry. (Alive cat) But if you don’t call, you’ll get your refund, some of which you will have to give away which you can never get back, and you will always have to worry that you will have to pay them back that money that you can’t recover. (Cat might be dead, but you wanted that money so bad you won’t ever know, unless he dies and the IRS notices - which they probably never will).
Honestly, the scenario where you point out the IRS’s mistake is the least likely outcome here. If you call, you’ll probably keep the refund. If you don’t call, you’ll probably keep the refund. It should all depend on how much it’s going to mess with you worrying they will come back to get the amount they gave you on accident.