It's not standard, I've only ever seen it on a Mac UK keyboard. According to Wikipedia the section symbol is only a physical key on a few keyboards: Mac UK, ISO Switzerland and ISO Sweden [0] Most standard ISO keyboards don't have it, including ISO UK.
> The button to the left of the 1 is the standard button on both EU and US keyboard layouts
It's very different on different standards and different languages of those standards. Mac UK and ISO UK are completely different, Mac US and ANSI are similar so I'm guessing you are using an ANSI layout.
> As a programmer, I'm using ~ daily
On UK ISO ~ is to the left of the return key i.e the majority of keyboards in the UK, not the 1 key (aha pun) which is where ANSI puts it.
The OPs keyboard is a Mac UK layout (most easily identifiable by the completely difference positions of @"\#~`), so the GP's comment is fairly accurate, weird mac squiggly thing indeed. They should really consider offering an ISO layout unless they are only targeting Mac users.
[0] https://en.wikipedia.org/wiki/Section_sign#Keyboard_entry