Trying to understand the Pokewalker

[Riku]

God help me. I have walked 6600 steps with my Machop through the Rugged Road and obtained 360 Watts, so that's 36 turns on the Poke Radar, according to serebii I should have a 50% chance of finding a Magby as my Machop is fighting type and I've done over 5000 steps. Yet on all 36 tries I didn't get a single Magby. I find this impossible to believe and now severly doubt what Serebii says can anyone try and explain this to me, I doubt this is down to bad luck, I also didn't see any Ponyta's which I was also trying to find and no Geodude's either.

 

[Falconwing]

Sorry, all you will find then are Onix, Machop, and Hoot Hoot. You only get three pokemon per stroll.

 

[Riku]

So if I returned from stroll, then sent the same Pokemon back, then the Pokemon that appear would be different?

 

[Battaman]

Some should differ, yes, however some will probably be the same, and it's not certain that will change, but it is the only way to change.

TL;DR, yes.