People were knew of robots in the 1930s. They were afraid of them killing humans and taking their jobs.
People in the 30s were afraid of anyone who looked slightly different to them because they might kill humans and take their jobs. And then some fucks actually killed humans and took their jobs out of fear said humans might kill humans and take their jobs.
FWIW, I never thought he was literally trying to choke him. Get leverage on him? Pop his head off?
Maybe they had Rock 'em Sock 'em Robots in his time
For those curious, it came out in 1964. One of the clues that it wasn’t made before the 1950s is that it is made of plastic.
Source: https://en.wikipedia.org/wiki/Rock_'Em_Sock_'Em_Robots
Its probably never a good idea to just let a super soldier wrangle with your neck though. Cap could without a doubt do some kind of damage there.
I’d also add that the head overall requires a decent amount of articulation which makes it a weak point and easier to cause damage to Ultron.
Also there’s important sensory and processing components making it much better to rip off than an arm or leg.