I read somewhere on the forum about another case like this, I believe the consensus was that the wrinkle tank was likely damaged when the bike was transported from Japan to the States (or even at the dealership), and the tank was most likely replaced by the original dealer with an off-the-shelf brand new non-wrinkle tank before the bike was sold.
I can only imagine the dealer's wholesale price of a NOS fuel tank in 1969 was probably in the $30-40 range so if one of their employees knocked one bike over and the bars dented the tank of another bike, it wouldn't be a huge deal to swap it out with one from the back room shelf.
It is more than "possible"... I knocked a KX250 over a few years ago when my air tool hose got caught on the MX step stand... of course it dented the tank on one of my nice personal bikes. Unfortunately I had neither a low cost new one on the shelf... or an employee to flip out on!
Regards, John