is Ninon Flash compatible with Pentax cameras?

[space-time]

I thought each major brand had their own version of hot shoe for flashes, and I thought you could not mix different brands, i.d. you could not use a Nikon Flash on a Pentax body. I saw this on CL and I now I wonder if my understanding was wrong and if in fact you can use a nikon flash on a Pentax body?

http://cnj.craigslist.org/ele/3464293345.html

FULL KIT WORTH MORE THAN $1,100
Pentax ZX-L 35mm SLR Autofocus Camera + Sigma 28-80mm Aspherical Macro Lens + Sigma 70-300mm DL Macro Super + Hoya Skylight Filter for both Lenses + Nikon Speedlight SB-50DX Flash + Sigma Camera Bag + Lens Cleaning Kit + Complete with Original Manual for Camera, Lenses & Flash - worth more than $1,100