Actually, you can jump over these enemies, even at ground level:
However, it's pretty difficult to do so. The triangular enemy head is probably just pointy enough to fit in the gap between the player character's legs, leaving you with window of one or two pixels where you can jump over them without triggering a collision.´
On a sidenote: shifting into the redblock right at the start and walking to the right made the rest of the level unplayable, as the player character simply disappeared. A reset button would probably be useful.