Is a puzzle box considered locked?

As part of some treasure the party I am in found, we found a puzzle box. I am a wizard, and I wanted to use the spell Knock to open it. Knock says:

Choose an object that you can see within range. The object can be a door, a box, a chest, a set of Manacles, a padlock, or another object that contains a mundane or magical means that prevents access.

A target that is held shut by a mundane lock or that is stuck or barred becomes unlocked, unstuck, or unbarred. If the object has multiple locks, only one of them is unlocked.

(emphasis mine). None of my party rolled high enough on an Investigation check to manage to open the box, and I said I wanted to cast Knock to open it. My rationale was that each step of the puzzle was a lock, and if I casted Knock enough times, it would open the puzzle box.

However, my DM said that the puzzle box isn’t technically “locked”. My thought was that since Knock will unstick or unbar doors, the item doesn’t need to be technically locked with a physical lock, it just needs to prevent us from opening it. I did not want to fight about it, so I dropped it, but I was curious if there is an official ruling. However, I did read this post and I’m not sure if the top answer agrees or disagrees with my specific situation.

So, can Knock open a puzzle box? If so, would it take one casting total, or one casting for each step of the puzzle?