How would the developer think that people would find the game without a fitting tag? I had a quick look at the three or more tags used by those, and I often see those .tap files zipped.
So my guess is, that there are some games that are tagged zx spectrum, but only have a windows version. But all the projects that can be played on the retro console also have these tags. Filtering for .tap would not do you any good, but remove those projects from your search that have the tap files zipped.