If you don't have an IRS PIN , it might be them just checking it is you that filed.
They will cash a check without regard of the tax return, but at least you have proof they got it.
Incredible how stupid the IRS is, like you say if you haven't moved and other things are constant, like bank account #, income sources, etc.. it probably is you.
Yet, the IRS page does talk about all this and even says you would have to show up with proof so they can do your return. Again the stupidity of the IRS is they don't put a phone number on the web site. Instead they say call the number on the letter.
So any scammer can send out letters looking the same with their own phone number and trick people into phoning in with all their Personal information.