“Racer” was pretty accurate though – the bikes were similar in design to those used by people who raced. “Road bike” could cover any bike designed for riding on the road, so is a much less precise description.
Back in my youth it was either a general purpose bike with 3-speed, mudguards, and a chainguard (Triumph Palm Beach) or it was a “racer”, with drops and derailleurs. Of course racers didn’t race but the term “racer” best expressed the features that distinguished them from heavier, more upright bikes.
By about 1990 you couldn’t buy a general purpose bike – it was mountain bike or racer, though racers rarely raced and mountain bikes sometimes did. But mountain bikes were meant for off road and bikes with drops were meant for on road. So the distinction was better expressed by the term “road” bike.
So it’s all quite logical really.
And we still spell neighbourhood correctly round these parts.