As regarding the actual meaning of Kawkab, in contemporary Arabic(MSA) it refers to planets and NOT stars. Not sure about the meaning in Classical Arabic and if it was any different.
I don't think the ancients were always able to distinguish the difference from stars and planets as planets usually look identical to stars in the night sky.
Definitely the Greeks knew what planets were, and probably the Babylonians too as they were keen astronomers and astrologers. But we have to remember that these stories were originally Hebrew, not Arabic. The word "Kowkab" is quite an early Semitic word as it is the same in both Arabic (كوكب) and Hebrew (כּוֹכָב).
Whatever the word means today in Arabic is irrelevant, the earliest version of the story is from Hebrew, and there the word simply means star, which probably includes both planets and suns in other solar systems, because to the non-expert they look the same in the night sky.