All the hypothesis you make seem plausible to me, I'd add that maybe he might have found a writer with animation/modelling skills too that will help on that too (to explain the PC).
The other part that also need some work is the update system, it can require some programming work to deal with connections, checksum and so on to have a smooth updating system (provided that there are not already off-the-shelf solutions). Not something so exciting to justify the waiting but it is nevertheless a part that needs to be done. But for sure nobody needs a rig like that to do this task.
In the case he hired someone (whatever the job is), buying a new PC is another "strange" choice: is she/he working physically together with him? That would mean he found someone in his city or not so far from his place that can easily commute, I don't think that someone will move from another region/country/continent for this kind of project. Minor detail, but let's not to forget this little covid problem with possible new lockdown/restrictions ahead that may prevent displacements.
Or maybe he is assembling the pc to be an exact replica of his and then ship it to her/him?
We know that he is obsessively secretive about his assets, the story and the way he works. Having someone physically working with him might reassure him, even if that does not prevent possible leaks etc.
The other (crazy) possibility is that he will force the new hire to work remotely on his new machine, so that everything stays under his control in terms of security. Needless to say, it won't be the case, because files can be "extracted" anyway and he will be more distracted controlling what's happening than working on his part of the project. And, no matter how good the internet connection is, it would be a nightmare for the other dev working like that.
He can use the second rig for the other dev to render his work remotely, because e.g. the other dev has no enough computing power in his hands. It can be the case, as the fan art thread shows, many good artists with great skills but limited by their available resources. That requires him to trust her/him with the assets, though.
Finally, I don't think that having two PCs for himself will improve anything in his workflow, this has been discussed ad nauseam in this forum.