Note that there are differing interpretations of "swirls". Anthony uses the classic definition, i.e. that "swirls" are "buffer swirls".
It seems that most people use the term to mean any kind of circular/elliptical/etc. marring, making it sorta interchangeable with "spiderwebs"/"cobwebs"/etc. These are, IMO, 99% the result of wash/dry techniques. The trick here is to a) use nonabrasive wash/dry media and b) move the potentially abrasive dirt off the paint without pressing it *against* the paint in the process, easier said than done.