Hopkins' contract was "cut friendly" ($3 Million dead money with $11 Million in cap savings), so the Texans may have been thinking about dumping him one way or another after all his complaints about his pay. This looks suspiciously like a straight-up salary dump. The Texans gained nearly $10 Million in cap space, a serviceable RB who might pull a Derrick Henry and a 2nd round pick instead of nothing if they just cut him.
The Cardinals get a great WR who seems to disappear in the playoffs and is grumbling about his contract. For them, the money is a wash.