I imagine you've ABXed this?
Regardless, the clip's spectrogram makes it clear it was an MP3 at some point (mastering engineers on crack?):
I ran it through aucdtect and it didn't give me a straight answer - "Could not qualify the source of this track."
Also, could you clarify what exactly this distortion is you're hearing? Is it sort of a teeth-brushing sound? Because I don't hear any difference beyond -q 3. I might just not be looking in the right place.
[OT]Can you know this from the looks of this spectrogram picture?? Do other lossy encoders have specific patterns too? I'd love to learn more about that. [/OT]