My hypothesis, as someone who doesn't work on AMP, is it forces people to copy/paste the boilerplate rather than writing their own version (and maybe getting it wrong).
I think he's implying the use of an emoji in the html tag is kind of ridiculous. Personally, I'm split being it being ridiculous and being pretty cool.
edit: Well, that should have had a weird lightning symbol next to the <html but I guess HN ate it up. See the example:
https://www.ampproject.org/docs/get_started/create/basic_mar...