Was Ravana an atheist?

I was under the impression that Ravana was a devotee of Lord Shiva, but 1.3.22 of Shrimad Bhagavatam says he was an atheist:

In the eighteenth incarnation, the Lord appeared as King Rāma. In order to perform some pleasing work for the demigods, He exhibited superhuman powers by controlling the Indian Ocean and then killing the atheist King Rāvaṇa, who was on the other side of the sea.

The only explanation I can understand is translating Adharmi to atheist, which is inaccurate.

P.S: The aforementioned translation is from Vedabase (ISCKON).