Most likely Kirby will be fine, but not a risk I would take for the sake of a phonecall...
I'm not one to go rushing to the vets every time my bird does something weird (we'd end up living there!) but I would agree with silver sage on this occasion- not saying rush him to the vets but I would want advice from an expert.
The clay won't be toxic, the issue would be that it clumps. You say he's eaten a hard lump of absorbant clay- that's going to absorb moisture inside him and clump and 'set' inside him. Whilst it is only a small piece he has eaten, he's only a little bird and it's relative. If he has chewed it then it will be broken up and will reclump inside him and can cause all sorts of problems, which could take days to show symptoms. My mum had a cat die from a few mouthfuls of cat litter which clumped inside him
