Probably a typing error, because every language newsletter is different (e.g Portuguese vs English).
I asked this (your) question according to the received Lingvist's Portuguese newsletter (announcing 5000 instead of 4000 words) 16 days ago: https://lingvist.com/forum/topic/810/your-3000-words-cutting-announcement-with-lingvist-free
@Lisa-Lingvist When will German be expanded? I've been working toward the goal of 5000 words for a couple of months now, and just bought a quarterly-paid registration for the premium version with the idea that I could reach 5000, only to discover after a few days that it only goes to 3941. Reading the subscription section of my account details I now see that it says "up to 4000". This was my mistake not check the terms more carefullly, but should have been explicitly addressed that you haven't created enough cards yet. Something like "We know we've given you a goal of 5000, but for now we don't have that many" because when you're practicing every single day, watching the progress bar get closer to the goal of 5000, you kind of assume that the app allows you to reach that goal.