Orwn, the adjective βαρύς (heavy) often has a negative/offensive connotation when used with smells, but the actual words to convey that negative connotation are at the discretion of the translator. So you're right--there's nothing inherently "evil" in that word.
Here's a literal crib of the part you care about
τὸ δὲ ἔλαιον (and the oil,) οἱ Πέρσαι (the Persians) καλέουσι (call) τοῦτο (it) ῥαδινάκην (rhadinakē), ἔστι δὲ (and is) μέλαν (black--neuter, in agreement with "oil") καὶ (and) ὀδμὴν (smell-) παρεχόμενον (furnishing) βαρέαν (feminine, in agreement with "smell"--literally, "heavy in weight"--when used of "impressions on the the senses," though, the lexicon says that the word means "strong, overbearing, or offensive").
Click on the links below if you want to see the full dictionary entries for the last three words:
hand over, furnish, yield, exhibit
βαρύς, εῖα, ύ,
"heavy"--Go to section III.2 of the definition and you'll see this very passage. Heh.