I would imagine Twitter would have access to analytics that third parties don't have, which would allow them to pretty easily work out which accounts are logged in and used for browsing and which are actually abandoned.
Opening a Twitter link in a private tab is the low complexity solution, or there's nitter.net, or deleting cookies, or various browser extensions that delete cookies for you.
After posting that, I went back and retested. It looks like they have swapped back to a soft nag popup. For a few months it was hard blocking any further scrolling, at least with Chrome.