What you're seeing are default avatars for new Twitch users. Curseforge required you to merge your old curse account and a Twitch account some time ago.
Even after you've merged your account, you used to be able to log-in to the forums with your old account and just ignoring the message about using your Twitch account instead (after logging-in, just open a new tab). Or in my case, never logout and don't delete cookies, thus remaining logged-in forever.
But as of yesterday, it seems like the system now uses your Twitch username and avatar regardless. All these users whose new avatars you're seeing probably have created a Twitch account in the past for the merger and never used it.