Is this the same as the Gadget • Difficulty X keywords? Or do they mean something else?
Yes. Gadget 6 & Gadget • Difficulty 6 are the same.
A templating change was done to bring Gagets in line with the wording on Spells.
Gadget X was chosen to signify the pull because:
Gadgets have to be invented by a Mad Scientist by default.
Having Mad Science X on that section of a card imbues the skill itself.