It's one of those web things, without a prompt it feels like any site ever could just recording through the mic and saving it.
Didn't you have to click the mic icon before it started recording anything?
Yes, but I don't know what the mic icon is. Does it just call a function? Is it a Chrome-provided icon that is always on top? Can the menu that is shown be edited by the website?
It calls a browser function, not a javascript function.