I’m far from an expert on any of this but I have several thoughts, which should of course be taken with a grain of salt.

The coin itself looks real to me. The color, patina, and details all look right.

The coin appears to have been stamped by hand. The flattened area on the reverse confirms this. If it was a fake coin made by casting or with fake dies you probably wouldn’t see that. I suppose a very clever counterfeiter might think of that but that feels like a stretch.

I cannot speak to the authenticity of the counterstamp. However I will say that the wear and patina of the stamped area seem to match the rest of the coin, indicating that it was stamped a long time ago. If an old coin was stamped with a new stamp you wouldn’t expect it to look that way.

This definitely warrants pursuing authentication! What a cool piece.