The website explicitly disables it; they have a viewport meta tag with:

    initial-scale=1.0, minimum-scale=1.0, maximum-scale=1.0, user-scalable=no

I think it's more likely Safari these days just ignores this, because of the very problem OP complained about.

Yeah, I actually think Safari has the right behavior here. I use zoom features all the time on all my devices.

I actually prefer pinch zoom than developers implementing accessibility features which often don’t test all hardware and get glitchy at certain zoom levels.