"Pace yourself" doesn't specifically mean "slow down", it actually means to maximize your speed across the full race. In other words it can mean speeding up when you look at the average pace across the entire event.
Yes, and pacing also stops you running too fast at the beginning of the race and blowing up. I believe "we can finish the overall race faster" is part of the metaphor they were aiming for.
Nah, they just want their competitors to slow down.
It does, but "pace yourself" is something we say to kids (for example) to tell them to slow down because they're going too fast. We don't tell people to pace themselves because they're going too slow.