Here's a spec comparison against the base model (it doesn't name it, but surely that'd be the RN) and the Grande. Looking at prices, the Grande was cheaper than most, and only a couple of hundred dearer than the RN, so it may well be an RN with a few extras thrown in cheap.
Just a quick run down on the differences, the Grande appears to get:
A radio/CD (in lieu of a radio/cassette)
A sunroof (presumably the manual tilt only one that's common on Clios)
And a few other bits and pieces.
If your car has these features, then it probably really is a Grande. If it doesn't, then you were ripped off and flogged an RN. If it has some but not others, then we're heading into unknown territory (or the specs on that website are wrong.) Unfortunately, Renault are renowned for changing their car specs more often than some people change their underpants.
Hope this helps
Edit: Not sure why I didn't think of this before, but I've just Googled "Clio RN Grande" and it has turned up loads of hits. It does appear that this was a special edition based on the RN.