Ignited TNT sticks to slime blocks when they are moved. To replicate you can use a dispenser filled with TNT then activate to drop on slime block, and when pushed the TNT will stick, or be pushed 1 block, or will be pushed backwards into the slimeblock, or even float in air next to slime block.

The screenshot with works writen on it actually pushes the TNT correctly since it doesn't have a slime block to stick to.