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Distagon is a formula for wide angle lenses

No, distagon is a formula for reversed tele lens designs.

That lens is much bigger than other 50mm FF lenses,

Yes, it is bigger than most 50mm designs.

about the size of a medium format 50mm

Speed boosters attach to FF lenses and converge the light onto APS-C area

"Speed boosters" are wide angle converters. A tele converter makes the FOV more narrow, and the resulting focal length / aperture ratio smaller. Wide angle converters make the FOV wider, and the resulting focal length / aperture ratio bigger (hence the silly term "speed booster").

 

For this lens to be a MF lens with "speed booster" the MF lens focal length would have to be much longer than 55mm (for the "speed booster" to turn the whole optical system into 55mm).

The groups do not look like a longer lens with a wide angle converter at the camera side either.

 

Like the name suggests, it is a reverse tele lens design.

 

This is a reversed telephoto lens, consisting of a large negative lens in front of an ordinary lens.  This allows it to obtain a short overall focal length with elements of a larger and more manageable size, helps design a system that is favorable for both high relative aperture and wild-angular field, and increased the back focal distance beyond it's usual magnitude, which give space for the mirror of a SLR. The downsides are that is must be physically large, and of complex construction to correct all the aberrations, making the lens more expensive to produce.    Reversed telephoto designs are rarely over 2 inches in focal length, and then it is only used for specific applications.  Compared to the Biogon, it has a larger circle of illumination full aperture, though softer when wide open, though it is sharper when stopped down. Rear element does not interfere with mirrors in SLR's

http://www.panix.com/~zone/photo/czlens.htm

 

Distagon means wide angle (lens) with large distance to the image. This applies to 55 mm lenses on 135 format SLRs too, because with 44-46mm flange distances retro focus designs are needed. Anyhow, my point was that if there was a "speed booster" design at play, the "original" MF lens would have to have a longer focal length, making it at least a normal lens, not a wide angle lens.