The website uses SVGs for animation instead of the canvas2d API, I'm fairly certain that's the cause.

(honestly I love SVGs for static images or at most one or two animations when used on a web-page, but if you're not using canvas2d or even webgl with a thin shim for anything more complex than that, mobile users will suffer)

For me animations mixed with text is bad UX. Would be better with buttons to start the animations when you have read the relevant paragraph.

Basically auto playing anything for me is bad UX.