This whole thing was very weird.
The anti-union ad was running TV ads all over Jackson area (even though only Nissan employees would be voting), putting up road signs and billboards, etc. I assume they were just trying to raise awareness of "oh noes unions are trying to come to Mississippi!!" rather than seriously trying to reach the random employee who might live in Madison (93% white rich suburb) or on Lakeland Drive in Northeast Jackson.
I didn't have a prediction for the vote, but the plant is 80% black and all of the local black political leaders were publicly on the "Yes" side, so I kinda assumed it would pass.
Which means that economic populism doesn't actually resonate?
I don't know that this is proof of that. I think the conclusion is that the Nissan employees were happy enough in their job and didn't see the benefits of a union outweighing the drawbacks (which may or may not have been real), such as the plant closing or all of them getting fired.