I can guess what your uncle rode because a small car is about as economical as a litre supersports bike which will do 0-60 in under 3 seconds.It's just that I had been toying with the idea of getting a smallish motorbike like a 125 to commute on as a cheaper alternative to the car but my uncle who was a keen biker before he got married (!) was insistant that a small car is just as economical, warm, dry and safer. It surprised me, to put it mildly.

My Fazer 1000 is as economical as most small cars (if I ride it that way) and return 50+ mpg. If I ride it at the same speed that small cars travel, I can get over 60mpg.
Most 125s will get 80+ mpg, some can get over 100. That's in normal use on real roads, not in the sanctified environment of some European institute which comes up with the frankly ludicrious "manufacturer's figures".