This is my job. I’m a staff level software engineer who previously worked at Google. My entire career has been writing Android apps.
Permissions are integral to phone app development and contacts is a specific permission that is heavily locked down.
So yes: I can possibly know and I have literally read the source code.
Unless you’re trying to insist that Discord developed a new 0 day that lets them bypass both Android and iOS operating system locks and then decided to use it to scrape contacts while giving you an option to turn it off?
Cause if that’s your supposition you’ve got a bad case of magical thinking.