Someone I know has the following for sale:

Canon 20 D
Serviced annually by Canon in Bangkok and lovingly taken care of. All firmware up to date as of last year.

Tamron 28/300mm XR-DI-LD
Serviced and checked by Nikon in bangkok a few months ago.

4 compact flash cards.

3 Canon batteries + canon charger

Camera bag and some filters

Appraised by Photo Bug at 24-26,000 - will accept 23,500. If you're interested PM me and I'll put you in touch. Less pixels on hand and a smaller LCD monitor but a better bet than the entry level Canons since it's got the wheel control on the back.

Am I mis-reading this? A Canon camera with a Nikon lens?

Your post said "Serviced and checked by Nikon "

and

B&H Photo says: Tamron Zoom Wide Angle-Telephoto AF 28-300mm f/3.5-6.3 XR Di LD Aspherical IF Macro Autofocus Lens for Nikon AF-D

Am I missing something?

Yes.

Third party lenses are made with mounts to fit popular cameras which doesn't always include Pentax I'm afraid. You saw Tamron lens to fit a Nikon but this one fits his 20D. I guess it doesn't matter who services the lens - just a matter of convenience.

that makes sense to me as I actually do have a Tamron 28-300 lens for my Pentax.