As someone who was living in the UK during the "minidisc era", I can confirm that this is extremely not true. Everyone I knew had a minidisc player, and they were ubiquitous while commuting on the tube.
I think the "it was only a success in Japan" meme is one of those things that people read on the internet and just assume is true because it sounds plausible. In reality they were very popular across Europe, wide parts of Asia, and Australia/NZ (to perhaps a slightly lesser extent) as well.
Anyway the YouTube video above covers all this better than I can.
