I have heard several people use it for that umbrella term, particularly back in the days when I lurked around following the WHATWG and CSS mailing lists.
Consider that much of what is new in HTML5 vis-à-vis HTML4 is in the changes to its JS APIs (e.g., <canvas> is all about the JS API), and its requirement that browsers support other standards such as SVG. Actually distinguishing which component of the web stack actually has a particular improvement that you seek to use doesn't provide all that much value... what does it matter if it's really the WHATWG HTML spec that mandated it or it's the ES5 spec?
Instead, you can just call it all "HTML5" and understand that it's using newer technologies that won't work on legacy browsers, although we're now so far deep into the era that we don't have a terminology for what requires a 2020 browser versus a 2015 browser.
Consider that much of what is new in HTML5 vis-à-vis HTML4 is in the changes to its JS APIs (e.g., <canvas> is all about the JS API), and its requirement that browsers support other standards such as SVG. Actually distinguishing which component of the web stack actually has a particular improvement that you seek to use doesn't provide all that much value... what does it matter if it's really the WHATWG HTML spec that mandated it or it's the ES5 spec?
Instead, you can just call it all "HTML5" and understand that it's using newer technologies that won't work on legacy browsers, although we're now so far deep into the era that we don't have a terminology for what requires a 2020 browser versus a 2015 browser.