Its Completely Author’s decision if he want to refund or not. You bought the HTML template , the title of product the price, the description everything states it clearly its not a WordPress theme.
Just like now you are too curious for your money means cannot spend 50$ if you were this much worried you could investigated more before buying the theme.
The template also have a WordPress version you can ask the author for refund, if he do then its good if he refuse, you can ask him if you buy WordPress theme then will he refund the amount or not in most cases authors accept refund this way.
Please note there are several buyers who buy HTMl templates then they say we bought it by mistake we wanted WordPress theme. I am also victim of this. I am not saying you are trying to play same game but this is the reason authors rarely accept this excuse to refund.
I hope you understand. thanks.