If your finger get tight, then suddenly snaps open, is that a dupytren contracture or some sort of trigger finger?

Triggering. What you are describing sounds like "triggering" - which is the classic sign of a trigger finger. See your local orthopedic or plastic surgeon about correcting this. Dupytren's has more of a band-like tightening, and doesn't "release" like you described.
Locking finger. A trigger finger is a finger which has stiffness, locking and clicking secondary to swelling of the flexor tendons.
Trigger finger. Snapping and locking in a finger is likely a trigger finger, especially with the sensation tightness in the digit. A dupuytren's contracture is a gradual flexion of the finger which can not be opened or straightened. See a board certified orthopaedic hand surgeon for evaluation and treatment.
Trigger Finger. A nodule at the flexor tendons, catches the a1 pulley in the palm. Most frequently.