That is VERY interesting - I wonder if that relationship applies now in Canada, as right now AFAIK, Mazda Canada is aligned with Petro-Canada for their lubricant needs.
Well Castrol seems to do it with more than just Mazda. My Triumph motorcycle had a sticker on the engine when it was new that said "Lubricated by Castrol" and in the manual it gives the oil specs and then says "Such as Castrol 10w50"