Is this a joke?

If not, HTML5 is normal HTML, not even a requirement to support IE8 will stop you using HTML5, though individual things in the various standards have different levels of support, and not all fallback gracefully or have polyfills available.

There's some starter kits that you can use that will provide the basics of an HTML5 site, like https://html5boilerplate.com/ or Bootstrap.

If you're not willing to learn or be adaptive to your customer' needs then you have no place creating websites as a profession

Its not me doing a HTML5 but does the website require is more of a question.

Using HTML5 or not makes no real difference for simple pages, so why wouldn't you do it? As far as I know it doesn't really have downsides.

If they mean something more than just HTML5, figure out what exactly they mean and decide about that.

You can go ahead and use HTML 5 compliant markup. As these are static websites, you won't need any Canvas or other advanced stuff.

This is a max 10 page static website, no db etc.

Why do they mean by HTML5? Semantic markup? CSS3 Animations? Audio or video maybe? Or did they just hear the buzzword and find it cool? It's your job to explain them what it is and what it implies. But technically just using the correct doctype means you are doing HTML5...

Their requirement is a static webpage and to have HTML5 ("As they say") on a static page? There is no media and/or animations etc