Is he pooping normally and as much as before? Is there bile in his poop? Is there hair in his vomit (in your previous thread, I believe he was always throwing up hairballs)? Is there hair in his poop?
I've forgotten what you previously said about the frequency of his meals, so if he isn't eating frequently enough - which the need for frequency/quantity can significantly vary by cat - that can cause bile build up in his digestive tract. Older cats’ digestive systems seem to do better with smaller, more frequent meals; and, for some cats, that can pose more digestive issues when they don’t get to eat that way.
Bowel motility can play a role in vomiting bile, but theoretically, you should see a change in his bowel habits - not to mention a negative change in his eating habits as well.
I've forgotten what you previously said about the frequency of his meals, so if he isn't eating frequently enough - which the need for frequency/quantity can significantly vary by cat - that can cause bile build up in his digestive tract. Older cats’ digestive systems seem to do better with smaller, more frequent meals; and, for some cats, that can pose more digestive issues when they don’t get to eat that way.
Bowel motility can play a role in vomiting bile, but theoretically, you should see a change in his bowel habits - not to mention a negative change in his eating habits as well.