Not an error, that's what some of the S mint marks looked like that year. Use the search box at the top of the screen, or Google, to see the difference between Type 1 and 2 1979 Anthony dollars.
In 1979 there were both uncirculated and proof SBA dollars with an S mintmark. The 1979 S circulation issue was not included in mint sets. Only the P & D were included. This appears to be a circulation strike, therefore, I don't think the TY 1 or TY 2 S mintmark is relevant here. I am pretty sure the TY 1 or TY 2 is for proof only.
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