It's an interesting picture. It's black and white, and truly looks like a vintage picture. The workers appear to be dressed in white uniforms, and wear sandals. If you check Kevin Mahoney's 2008 factory tour video you'll see that Royal Enfield workers these days dress in shirts of various designs and wear shoes (probably a safety requirement).
The motorcycles in the "1965" picture are being assembled on old-fashioned carts that are not seen in the 2008 video. The motorcycles are kick-start only, as certainly would be the case in 1965. They have the left-side brake pedal, so the five-speed transmission has not been made standard yet, either. Again, 1965 could be the correct year.
But here's something I find strange: the tanks are labelled "Royal Enfield." I thought that the factory in India used only "Enfield" prior to 2000. My own 1999 Bullet is just an "Enfield."
Jorge Pullin's blog, My Royal Enfields, has a full explanation of how the company only went to court in 1995 to secure its right to use the full name "Royal Enfield."
So how can this be a 1965 picture? I asked the seller. He graciously responded:
"Please be aware that this photo was taken in India and Royal Enfield motorcycles were produced there under license. I obtained a large group of negatives that were all taken in 1965 in various Indian motorcycle and automobile plants and that is what I am selling on eBay. I would assume that since these were produced in India, they may appear to be slightly different than the British Royal Enfield models. I have no more knowledge of this than what I have told you. Sincerely, Walter Miller"Did the factory use the full name Royal Enfield on home-market motorcycles prior to 2000?