Since you've read about it online, let me try a different analogy.

Imagine an elastic or stretchy rope running through several pipes, and in between the pipes over pulleys. If you pull on the rope it will pull the pipes together and possibly into a curve made from the pipe segments.

Now suppose a pipe, or all pipes, get gummed up, or the pulleys stick with dirty bearings.

When you pull on the rope instead of sliding smoothly it will catch and resist the pull and stretch a bit or even stop, until the pulling force and stretch in the rope overcomes the catching, which is caused by the gummed up pipes and dirty pulley bearings. At this point the rope will suddenly pull through in the direction of the pull, with a jerk and the pipes will close up on one another into a curve with a snap.

Replace the rope with tendons, the pipes with tendon sheaths, and the pulleys with tendon pulleys and you have trigger finger. In the hand there are two sets of tendons, above and below the fingers or hands to close and open the fingers and hand.

There is usually no connection with DD, unless nodules or cords compress on the tendon sheaths and pulleys.