Hi David, it's hard to say without hearing the track! Maybe you used a pedal which gave the guitar a synthy quality? Just speculating. I've bumped into screeners who use "MIDI" interchangeably with "VST."
My instrumental rock, jazz, orchestral, and electronic albums are streaming now - Most include a link to download for personal or commercial use: www.douglaswaynericketts.com
Sometimes I get feedback like this outside of TAXI on my bass playing, even though I play the bass live on all my tracks lol. Almost every time this has happened though, it's because of the tone / pedals being used, and lack of dynamics in my playing. These two things together can make it sound "lifeless" aka be easily confused for MIDI. I haven't heard your track though, I'm just saying that's just the main culprit for me when this happens!
The screener is right about re-amping. I used to use a Radial reamp box until I got a Quantum HG interface. I still have yet to get a Rock forward though lol. One of these days!