I have made up a second and larger portion of this pudding, again using milk.
It seems to me that yes it does expand but only so far, so once done it appears at least that it would not expand any further, once in the stomach.
If one were to eat the seeds in their pre hydrated state (dry) like sprinkled on a salad or something then yes they would expand but only in a limited way and in small quantise presumably this would not be an issue.
I don’t know if this is correct but it seems to look that way.
I have just started making a batch of mixed berry jam using a frozen 5 berry mix and Stevia. I will use some chia seeds to help jel it up.