Not only that... they restructured Ben and at least one other contract I believe to create the cap space to do so. The Steelers are notorious credit card users when it comes to the salary cap... they constantly push bad contracts into future years.
Per Spotrac, even after accounting for Foster retiring and them cutting Mark Barron, they're still $8M over the cap currently. I know they converted Ben's salary into a bonus, which saves about $4.25M I believe, but they'll still need to cut another $4-5M at least in the next 24 hours. My guess is they'll decline Vance McDonald's option, which would free up about $5.5M, among other moves.
I've been telling people this all offseason about the Steelers... while I have no doubt they'll be better with Ben, they're going to lose some key role players on that team, they have virtually no ability to create salary cap capital to sign new players without cutting somebody significant (DeCastro, Heyward, Haden, Pouncey), and they essentially only have two draft picks in the top 100.
I don't see many ways where they have an improved roster in 2020, meaning they'll need everybody to play at a comparable or better level than 2019 in order to consistently compete. I have my doubts.
I also love the fact that Ben now has like a $36M cap hit in 2021.