Let's take it as read that Vison satisfies the requirements of sentient being. That rather simplifies the question. It's his own motivation that drive the desire to move the hammer, as opposed to someone operating him remotely.
Magic Spells are notoriously fickle. There have been endless discussion of the definition of the word "worthy", and whether or not it can change based on the situation. There's an argument that the spell, or perhaps the hammer itself, can "decide" if a person is worthy.
Beta Ray Bill picked up the hammer and received the power of Thor. His cause was just, his desire to good sincere, so he was deemed worthy.
The SHIELD agents trying to move the hammer were not deemed worthy; whether they moved it by hand or with machinery is largely moot.
Captain America budges the hammer by just a millimeter or so earlier in the film, far more than the rest of the crew. So while Cap himself is certainly as pure of heart and "worthy" as any person, at that moment he was trying to lift the hammer as a goof, perhaps even as an act of pride. So the hammer "decided" that the need was not worthy, and stayed put after the slightest moment of introspection, which allowed for the nudge. I know he's lifted the hammer in the comics (citation needed), and if, in the heat of battle, he needed it to same lives, or even just to throw it to Thor, there's every chance he could, at that moment.
At the moment of his creation, he has no hubris, no pride, and is only interested in doing good. He is not trying to use the hammer himself, only to hand it to its proper owner. Indeed, he's not even aware of any restriction about picking it up, so there's not even the chance of doubt creeping into his mind - "Can I do this? Am I worthy?". Looking at that moment, with that mindset, it's very likely that the hammer/spell would decide worthy = true. If he tried it again after the battle, he may not be able to, as the moment of need had passed.
