Since my carpal tunnel release I have developed trigger finger, could the previous surgery have set it off?

Yes. Hands often swell after surgery and triggering comes from swelling. On the other hand, many patients with carpal tunnel syndrome often have swelling causing the problem in the first place.
Yes, but not likely. Inflammation is common after any surgical procede. Swelling in the hand after carpal tunnel release may lead to inflammation in the tendons and tendon sheaths. If triggering occurs, oral/injectable steroids and therapy should relieve symptoms.
Unlikely. There is an association between carpal tunnel syndrome and trigger finger. One probably did not lead to the other, though the timing is often quite coincidental.