The distances were converted to degrees externally to make it possible to compose circles in data that is expressed in degrees.
That is a mistake. Degrees are not the same length all over the earth, and they are not even the same length depending on the direction.
Hire a boat and go to the intersection of the Prime Meridian and the Equator in the ocean off the coast of Africa. Draw a circle that has a radius of one degree and it ends up being about 110 km in radius. It actually looks like a circle, too, if you hover directly above it in your space plane a few hundred km above.
Now, fly to the North Pole in your space plane. Put on your parka and step outside, walking over to stand directly onto the North Pole. Step ten paces towards the South. That would be, of course, any direction from the North Pole since all straight lines leading away from the North pole are heading South.
Suppose one of your "paces" is about 0.6 meters. Ten paces means you've stepped about six meters from the North Pole. A circle with a diameter of 12 meters has a circumference around 37.7 meters. Divide that circle into 360 parts (one part for each degree of longitude) and you get a result of about 10.5 cm for each degree of longitude.
Ten paces from the North pole, one degree of longitude that was 110 km in "length" on the Equator is less than 11 cm in "length".
So now, standing ten paces from the North pole, try drawing a circle that had a radius of 1 degree. What you end up with is a very skinny ellipsoid shape, basically a line at the top and a fatter line at the bottom, which extends 220 km to the south (degrees of latitude are still about 110 km) but which varies from an east west "radius" of 10.5 cm near the top to an east west "radius" of about 1920 cm at the bottom.
That's because the east-west length of a degree varies from about 10.5 cm a few paces from the North Pole to about 1920 cm around 220 km to the south of the North Pole.
The moral of the story: In the Latitude / Longitude projection, using degrees as linear units of measure to specify the location of points each of which is one degree in distance from a central point, does NOT result in a circle. That is because in the Latitude / Longitude projection, the "length" of a degree varies depending on where on Earth that degree is located and also the bearing of that degree. Degrees of latitude are approximately the same, but degrees of longitude are not, so anything except measurements straight up and down, so to speak, will vary.
The shape distortion you report is an accepted and well-known consequence of using different projections. It is one reason why one should choose the right projection for the particular task they have in mind. See the discussion in the About Projections topics.