Small circles don't have enough points and render as polygons. This code:
import arcade
arcade.open_window(800, 300, "Test")
arcade.set_background_color(arcade.color.WHITE)
arcade.start_render()
x = 10
for radius in range(1, 30):
arcade.draw_circle_filled(x, 150, radius, arcade.color.BLACK)
x += 40
arcade.finish_render()
arcade.run()
Renders as:

Lots of complaining in my intro class.
Small circles don't have enough points and render as polygons. This code:
Renders as:
Lots of complaining in my intro class.