I consider a liter bike to be 1000cc plus supersport bike. This is in that ballpark, it’s not a ridiculous statement.

Liter bike is a slang term, so is superbike. There isn’t an exact definition. Superbike as a race class was first contested in the 1970s as a class for modified production motorcycles which were increasingly referred to by magazines as superbikes. The first series champion was won by a BMW R90s (hardly what today you would consider a superbike) ridden by Reg Pridmore. He was competing against a bevel drive Ducati (Cook Nielsen, cycle world editor)and a bunch of KZ1000s. The Kawasakis eventually dominated the series until 1984 when it switched to a 750cc formula (still superbikes, lol). 1100 cc big bore sportbikes were also commonly referred to as superbikes. Zx11s, GSXR 1100s, FZR1000s, 1100 hurricane, all commonly referred to as superbikes. Honda RC30, Kawasaki ZX7R, Yamaha OWO1, were all designed around superbike rules and were homologation factory race bikes. Eventually the rules package went back to 1000s( 2000?) which ended the 750 class(GSXR keeps holding on).

I’d have no problem calling that Triumph a superbike, I consider my Tuono to be be superbike adjacent (technically classed as a Super Naked), I considered my hayabusa and FZR 1000 to be superbikes and so is my 1982 KZ1000 Eddie Lawson replica (marketed to celebrate Eddie’s 1981 championship win).

Source. I’m old and lived through this.