Physics isn't disabled on Destructible when Simulate Physics is set to Disabled. The Destructible seems to only be set to sleep and will wake if the player or any other physics object touches the destructible.
Since destructibles are technically skeletal meshes, it is expected for them to behavior in a similar fashion as a skeletal mesh (which do work as expected where the skeletal mesh's physics is completely disabled).
There is a bug with destructible meshes when trying to disable physics simulation at runtime. It doesn't work as it should.
When trying the same with static meshes "Simulate Physics" is being properly disabled, and no collision nor wake up call will make the ball fall again.
My wild guess is that calling "Set Simulate Physics" on destructible component with false parameter just puts it to sleep instead of actually disabling physics simulation.
Results: The Destructible (which had Physics disabled) will wake and fall to the ground
Expected: For Physics to have actually been disabled and the Destructible to act as a static object
Head over to the existing Questions & Answers thread and let us know what's up.