Hypertext: is text displayed on a computer display or other electronic devices with references (hyperlinks) to other text which the reader can immediately access...
So it's a game engine that relies on something that is, according to definition a text-only language. Are you really into ASCII games? Otherwise the name is very misleading. For legacy reasons.
HTML5 - the number in the name is important, this is a brand that represents a set of supported APIs and tags (https://developer.mozilla.org/en/docs/web/Guide/HTML/HTML5). They are obviously not talking about the markup language itself.
They equally could've called it SQL256 or XML2000 and then explain that it doesn't mean what the abbreviation states. I guess there is no need to argue for us, but personally prefer names that reflect the nature precisely. At least this is how I name my programming constructs and projects.
I know it's stupid, but the other alternative is calling it "HTML5&friends Game Engine", like the Mozilla guide suggests... Technically correct, but just as vague and now it sounds like a kid's show... I think we can easily agree this is not an improvement :)
The real name, which is "HTML5 + JavaScript + Canvas API + WebGL API + Web Audio API + Web Workers API + jQuery (for good measure, not actually used) + CSS3 Game Engine", doesn't fit on a t-shirt and, when put in a title tag, probably crashes older browsers and causes a Google employee to come and manually set your PageRank to -1.
