Just tested mine and am unable to get a magnet to stick. Tried several types and ....nothing

Even when dealing with "stainless" steels, the nickel content you're going to encounter is generally no higher than 15-20%, with other elements like chrome, cobalt, magnesium, et cetera making up the rest of the trace content. In any case, you'll still be looking at no less than 70% ferrous material in a "stainless" steel. (I put stainless in quotations simply because most stainless steels are simply corrosion resistant, not corrosion proof. In practical terms for most people corrosion won't be an issue, but one should probably think twice before relying on these lasting years in salt water situations). Being at least 70% ferrous, magnets will be attracted. The only possible exception I can think of is H1 steel.

I think you both know (and care) a tad too much about the magnetism of your water bottles.

Cold working 18/8 can form subtle ferromagnetic characteristics. I'm guessing that Klean Kanteens are made from a blank using several dies, which could explain the magnetism. Just a theory.