Oh yes, and maybe his very presence in the hotel bar caused the teapot to be poisoned and he contaminated all these other people EXCEPT his family... yes, yes, very very very likely
If you really want to consider every possible explanation, why not include Putin's dog Koni into the mix: maybe he met the dog and they were planning some secret overthrow of Putin's regime with Koni acting as a nuclear turd-layer that would kill everybody in the Kremlin? Or better yet: maybe Litvinenko wanted sugar in his tea, and accidentally dropped a polonium lump instead of a sugar lump that he found in his pocket?
I seriously doubt this can be anything but murder. Especially when they have found extremely high concentrations of polonium on the teacup and the teapot and on the waiters in the bar. Who did it and why, I will give you the benefit of the doubt, but let's be realistic here. It seems like you are grasping at straws here.
Oh, and why should the tea glow? You don't seriously think that just because something is radioactive it has to glow? In fact, almost nothing radioactive glows.