It does look like some local unions thing. If there was an attempt underway to unionize the Tesla plant itself, they wouldn't picket over that, they would simply call for a NLRB-supervised vote.
Several unions (UAW, plus I think 2 others) tried to unionize Mercedes plant where I worked. They never could get enough employees to sign cards to get NLRB to authorize a vote. Many of the team members had worked in union settings before (steel, mining, etc.) and had a bad taste in their mouth for unions. I worked in a union GM plant for over 10 years - seemed like the union did everything they could to make life difficult for everyone at the plant - both management and labor alike. They had a vested interest in strife and conflict.
Most auto plants now treat their workers very well, with wages & benefits equivalent to union plants; so the unions no longer can claim they can provide all these things through collective bargaining. (Decades ago, manufacturing plants really were very hard on workers, so there was a good reason why unions started). I believe that the good treatment auto workers get today - in non-union plants - is due to the threat of a union coming in. Even though, like Elon, they say they are neutral, they know that a union makes a plant much less efficient due to the work rules. Anyone who has worked in a union plant can tell true stories for hours about the nonsense in these plants - it drives up costs dramatically and creates an unwarranted sense of entitlement for workers - to say nothing of the "us versus they" poisonous environment that can develop. I suppose there are unionized plants where management and labor work as a true team, but this requires both extraordinarily talented management and very enlightened union reps - which is often not the case.
So, I'm in favor of unions - as long as they are entrenched in my competitor's factories (and not in mine).