What surprises me is that bash is not syntax comfy but on this part they made a very ergonomic addition

I think they meant string interpolation, not format. SNOBOL looks like a very early example, not sure it's the earliest. Though the example there looks more like a demonstration of, I guess, automatic concatenation versus what most people think of as interpolation ("foo {bar} baz" or "foo $bar baz" or similar).

https://en.wikipedia.org/wiki/String_interpolation#Snobol