They send notifications to your phone whenever someone messages you. Those unread icons are addictive, at least for me I always have to actively think to not open them immediately.
That’s just the natural outcome of blurring chat rooms with social media.
That still applies for non-social media. My iOS IRC client connected to my znc bouncer also shows notifications. Same for iMessage which is more profile-like, since you can send memoji and stickers and play games with your friends (eg. GamePigeon), which is why the bill tries to exclude 'chat' apps and email apps.
How much different is IRC/Discourse vs Twitter? Hashtags are effectively channels. Twitter just has more subscribers and more individuals in each channel.
The question isn't whether you think they have an addictive algorithm, the question is whether a lawyer can convince a jury that they fit the law's definition of one.
I think the person you responded to was referring to Discourse[1] forums, not Discord[2]. Although I agree with you and the gp, both Discourse and Discord have very different incentives than traditional social media FB, IG, etc.