A deaf, drunk, disinterested and (or) out-of-tune guitarist is not the fault of backing tracks.
Glad someone else responded - from the extensive discussions of this show online, it
appears that Eddie picked up (or was given by a stage tech) a guitar in a different tuning. They usually (by all accounts) actually have a live keyboard player off stage--something Eddie decided to do early on. Other posts in that discussion revealed that on a later show in that tour, the keyboard part was in the same key as in this video. Hence the detuned guitar (which Eddie apparently uses for some songs) scenario being the most likely.
The only confusing part is why a musician of his caliber would continue to play the wrong instrument/wrong key without correcting it. Alcohol? Show must go on (as in, no one will notice or care anyway, or they'd notice the guitar swap as a more distracting thing)? Who knows.
But right, it almost certainly wasn't backing tracks.
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I used to play bass occasionally with a couple of stellar musicians back in the 80's. Both of them played keyboards and guitar and were excellent singers and entertainers--when they had big gigs or special needs (outdoor festivals, 70's rock shows, etc.) they could tap musician friends to join up, growing the band to 4 or 5, depending on the pay and audience. But they had a house gig for YEARS playing Top40 where she just sang and worked the audience and he played keys and guitar. Everything else was sequenced and triggered, and the crowds came back every single weekend. He wrote all of the sequences, they recorded their voices for BGV samples, and they were smokin'. As was mentioned, this was the time for this sort of thing, and the only way to get the right sound without a 10 piece with multiple keyboardists...
I often despair of finding the right musicians in my area for some of the stuff I'd like to do, so I respect those that have to fill a personnel gap electronically. I'm in an area where there's only one genre that serious musicians focus on, and it doesn't pay. I probably wouldn't sample and sequence horn parts for R&B/Motown, or a banjo for blugrass--but that's a personal preference. I'd play with tracks in a heartbeat for music like 80's Top40. Just seems not-inappropriate at all.