I really think that’s just a plug. I’ve seen those before, but I’ve never seen an anode in its own port that wasn’t a hex.
But your surmise isn’t right, either. Anodes are installed at the factory and never elsewhere. My guess is that if you unscrewed the hot nipple, you’d find an anode extending beneath it.
In the past, American has not used those, but now that they belong to A.O. Smith, which HAS used them, maybe they do.