The 3" format disks mentioned in the article where "common" in the UK on the Spectrum +3 (which had a built in floppy drive), I owned one at one point.
The lore is that the world was moving to 3.5 and Alan Sugar (who owned Spectrum brand later after Amstrad bought them out) got a huge job lot of drives and disks cheap so they used them for the +3 as well as the existing CPC systems that had them (in fact the +3 used a modified version of AMDOS which ran the drives on the CPC).
It wasn't a terrible spectrum but it was already very obsolete by the time it was released.
The Amstrad PCW word processor was also very widespread in UK offices, and that used 3" disks so there must be tons of letters, interoffice memos and other office documents out there in that format. Of course that's only half the problem, the other half is that it used a very strange word processor called Locoscript (https://en.wikipedia.org/wiki/Amstrad_PCW)
It's a myth. Amstrad computers were already using 3 inch drives in 1984, way before 3.5 inch ones became popular. The drives were chosen due to their similarity to 5.25 drives, so that existing controller chips could be reused. Due to the huge volume of ordered drives, Amstrad did get huge discounts on them, but that had nothing to with the drives becoming obsolete.
I was envious of my friends that owned one, versus my Timex 2068.
It had a much better BASIC, and CP/M was also available (CP/M Plus).
I didn't get the +3 til years after they launched and already had an "old" (not to me) Olivetti PC1 and not long after an Elonex 286 so the +3 was just games really for me at that point - once I got access to Turbo Pascal I had no interest in programming BASIC any more.
Same here regarding Turbo Pascal, however I first had to go through GW-BASIC and Turbo BASIC, with a bit of Z80, 68000 and 80x86 before getting into Turbo Pascal.
Between the Amstrad PC1512 at the school club, the other friends lucky enough to have Amiga 500 which organized demoscene like parties at their places, until I finally got hold of a 386SX.