I agree with Pete, but in answer to your question – in essence not really, but kind of. Let me explain…
By targeting something that’s at a premium price range you’re reducing the entire audience category, as you’d want to exclude ‘cheap bike’ keywords, but it’s not a ‘proper’ niche.
So what is?…
A ‘proper’ niche would be a much more targeted version of the general category of bikes.
So if we’re sticking with that example it could be bikes designed for racing, vintage bikes from 1920 – 1980 or bikes designed for city living.
Then you’d apply your price criteria and further divide the audience you’re looking for.
By doing the above you’re looking at what I’d describe as a ‘proper’ niche or at the least the start of it.
Hope this helps!