The definition for heathen: a person who does not believe in an orthodox religion. That does not mean - does not worship a deity - or have a religion.
I think its the Christians that are confused about the meaning of heathen - not most atheists. Non-belief in the "Christian God" does not mean that person is an atheist as the Christians seem to think because their Christian websites definition for irreligious (Synonyms) agnostic, atheistic, heathen, idolatrous, impious, infidel, polytheistic, profane (Antonyms) believing, religious. The only one of those terms that clearly means irreligious is atheistic. Agnostic (means no knowledge) but they can be theist. An infidel can be anyone who is not Muslim. The rest of those terms could be used to describe religions other than Christian but they do not have to be irreligious.
The meaning of heathen has varied over time, but it has never designated people with a complete absence of supernatural belief or a religion. Heathens are not atheists and the term does not mean atheist. Heathen is a different word entirely with a different etymology; Old English via Norse. The original Heathens were the pre-Christian North European peoples who lived a thousand and more years ago in the lands around what is now called the North Sea. These included the peoples of Anglo-Saxon England, Scandinavia, Germany and Frisia (Friesland). Heathen gods come from Norse Mythology.
Many scholars have found through extensive research that miracle-working sons of God, born of a mortal woman were common elements of Pagan religion that preceded Christianity. Heaven, hell, prophecy, sacrifice, baptism, communion, monotheism, the Holy Spirit and immortality can be found in earlier Pagan faiths. This came from ancient Mediterranean culture. Constantine worshipped the sun god Sol Invitus, the Romanized version of Mithra, until he died.
Read Ezekiel the eighth chapter, verse fourteen, and you'll see that Ezekiel referred to the women who were standing before the gate of the house of Jehovah, weeping over Tammuz. Tammuz was born of a virgin, Sumerian-Babylonian, savior-god, who died and was resurrected, and each spring, in this ceremony, the women wept and wailed over his death, and then a few days later, they celebrated his resurrection. It's a pagan custom. Christianity is based on pagan dates and calendar. Why is December 25 important in pagan lore (in the Northern Hemisphere at least). The answer is simple, the sun descends to its lowest point on the horizon on December 22 where it remains until December 25. That is, the sun reaches its lowest point for 3 days and then is "resurrected". The whole Christian story is based on this and other astrological events.
A belief in the supernatural is not atheistic. Atheists are not heathens and heathens are not atheists.