Here's an interesting evidential report for the techies to ponder.
I have a 93 SPI which I always run on Super Unleaded, mainly Shell. The fueling system is well maintained and the ECU keeps everything in tune. Following a full weekends driving I was returning home last night and the garage I chose had run out of super so I put £20 (16 litres) of normal unleaded in to fill her up and off I went. I hadn't got more than 3 or 4 miles down the road before all hell broke loose. The car started to Kangaroo and back fire violently. It refused to pull at all in 4th and was reluctant in 3rd. It was constantly missing and looking in danger of needing some roadside assistance. I was some how still able to keep it going and gradually it started to recover. It took a good 5 miles before it really ran smooth again. Once it had got used to the new mix it ran back home (70 miles) without a problem.
I think this supports the view that Super unleaded DOES make a difference. In this case the car was able to re-tune itself to tolerate the inferior mix.
I'll be returning to SUPER Unleaded POST HASTE.
Again ethanol content could be a factor I guess - the oxygen in the ethanol affects the required AFR, so the injection quantity required would be different. Also, although I have little experience of SPI, I believe that the injector sprays onto the butterfly valve - ethanol has different vaporisation characteristics so may act differently in this condition.
Alternatively, given the short duration of the issue he could have run the tank really low and drawn tank crud into the pipes ♂️