Because the first season of the series consisted of 52 11-minute shorts, the crew members had assumed that there would be two additional seasons of 52 11-minute shorts. However, Cartoon Network is splitting up the remaining 104 shorts into 26 cartoons per season, which allows them to proclaim four new seasons of content.
It’s not a crime for Cartoon Network to change the number of episodes per season, and in fact, some of their shows have 26 episodes per seasons. Also, the bulk of Uncle Grandpa — 100 cartoons — hasn’t even debuted yet. In other words, fans of Uncle Grandpa, Mr. Gus, Belly Bag, Pizza Steve, and Giant Realistic Flying Tiger can look forward to years of original new content.
But looking at it from the perspective of the crew (and that’s what we do because we’re an industry resource), CN’s announcement of two new seasons was disingenuous. We’ve never received a press release claiming that a show is being renewed, when in fact the entire crew is being laid off. It’s a savvy way for Cartoon Network to spin bad news, and avoid the negative press that often accompanies show cancellation announcements, as Disney has experienced in recent years when they wrapped production on Phineas and Ferb and Wander Over Yonder.
For those wondering about Steven Universe, Cartoon Network pulled a similar stunt on that series by reducing the number of episodes per season to be able to claim additional seasons. This was confirmed by show writer Matt Burnett on Twitter, who posted the following (now-deleted) tweet:

It’s not clear yet whether Steven Universe will extend beyond its “fourth” and “fifth” seasons.