The text plays on the double meaning of the words 'press' and 'release'. In one sense, they refer to the physical actions of pressing and releasing a button. In the humorous context, 'press' is also a play on testing something by pressing a button, while 'release' is unexpectedly linked to detonating, which is a play on the typical expectation of releasing being a safe action.
PRESS To test . < click > RELEASE to detonate .