I can only offer some conjecture about this, but it might be a start for you.
On this site - http://www.4crests.com/kugelman-coat-of-arms.html
- the explanation sounds plausible. However, I'd read on another 'coat of arms' site some years back that the 'Kugelman' was a foot soldier who carried and hurled a small spherical bomb (the word kugel variously refers to a variety of objects having spherical or rounded shapes). I'd say we need something more official, though, than a website tale, to say we know what our surname is all about.