I would say the seller is correct in calling it a Vitomatic I. These are all variations of the Vito B design.
This uses a match-needle system based on a selenium meter.
It is zone focus, because there is no secondary rangefinder window. This has a Van Albada viewfinder, so you should have framelines in the viewfinder. That's a plus, because you can get more accurate framing.
The helical simply are the focusing threads. With 50-year-old cameras, the lubrication often has thickened, which makes focusing tight. However, because it's a zone focus camera, it's not as big a concern.
The lens appears to be clean. Ask if the lens has fungus or mold, cleaning marks, scratches or haze.
Also ask if the selenium meter is still accurate. Forgot to add that part.
Looks to be a decent camera.
This is a Vito B, and you can see how the Vitomatic is based on this camera.