I did check with ABP enabled and disabled the other day, and I got same login screen in both scenarios. I must have done something wrong, because I just tried again with a Chrome incognito window with ABP disabled, and I was able to navigate the website without getting any screen asking me to login. So you are correct: this login screen is targeted towards users using ad blockers. New filter/s in the next few days. Thanks for reporting!
I have checked again, thoroughly this time. I looked through the website source code, and found no Anti-Adblock code at all. I ran several tests and discovered that you get the login screen after about 10 articles read. And you get this login screen with or without ABP. I believe the amount of read/accessed articles are being stored in a cookie, so if you delete cookies for this website, you can get another 10 "free" articles. This can also be accomplished by navigating this website within a Chrome incognito window or Firefox private window, since they don't store cookies by default.
CONCLUSION: the login screen appears with or without ABP, after about 10 read articles. Unfortunately, I will not add filters into EasyList Spanish to prevent this from happening, as it really isn't advertising and also it isn't targeted to users with adblockers. Apologies for speaking too soon in my previous post.