It's not a simple copy of a videogame, it's a complete remake with a different TITLE and, of course, it doesn't to be an official release and being endorsed by Capcom or any other company. It's just a 'fan made' conversion as many other freeware or shareware remakes from arcade or console videogames for the ZX Spectrum, that's all. Moreover, their authors possibly don't want to get paid for this piece of gold. As it's free downloadable (for now), there is no need to argue or complain, while this game may remain as freely distributed only if zxpresh desires it or not.
Since many years ago, many people (programmers and little software houses) released unofficial conversions of coin-op arcade machines, or just inspired in them and, as far as I know, nobody said nothing.