Laughter is provoked by a discontinuation of what your brain expects.
If you saw a dog walking a man on all fours, you would most likely laugh, because of the unexpectedness.
In this case, the unexpected terseness causes laughter. You don't expect what follows to just be "Eject". In a technical context like a manual, you expect what follows to be a detailed list of steps and instructions. When this expectation is shattered, you laugh.