Rather sounds like a misunderstanding of the dangers to me.
A can isn't going to explode or burst into flames merely from sparks or welding slag. Not even if you foolishly leave it right beside the welding operation. Put it right up there beside cars exploding from cell phone use when refueling.
In the event of an actual garage fire, the explosion of a paint can is rather minor. If you are storing large containers of things like lacquer thinner, those have a much more interesting explosive potential. In which case a heavy steel cabinet makes them into a bomb. So doing "the right thing" makes things much worse. Read it again and understand it, placing them in a heavy steel cabinet makes them into a bomb, and makes them much more dangerous. That's why you never see them in real prepared shops. You'd see true explosive safe cabinets that have very weak backs, opened to the outside of the shop through a wall. I doubt you actually want to go that far.
A wooden cabinet is actually quite fire resistent. Wooden boards don't easily ignite. That's why every boy scout knows about using tinder and kindling before adding large pieces of wood.