Is trigger finger in the thumb a complication of carpal tunnel release?

Not usually. It is not uncommon to develop swelling in the hand after a carpal tunnel release. Sometimes swelling can affect the tendons and tendon sheath. If this occurs, triggering may develope. It may also be unrelated. Carpal tunnel syndrome (cts) and trigger finger have overlapping patient demographics. Oral/injectable steroids and therapy should relieve your symptoms.
No. The timing may be suspicious: many people develop trigger finger/thumb after carpal tunnel surgery. However, it is well known that carpal tunnel syndrome and trigger finger are conditions that are often associated with one another.
No. But they may both be due to same underlying cause -- tendon swelling. Approximately 46% of patients with carpal tunnel also have a trigger finger.