Well done.
Excuse me? I went to College and then went onto University thank you very much.
Me too. Because I couldn't get into University without going to college first.
So you did College instead of Sixth Form then because you could have got in via that route. That's normally the way things are done in the UK.
I personally did my GCSE's at 16, did lower Sixth Form or AS level as they were introduced as that year and then did transferred to College after and then University after that.
The way you phrased it earlier, it's either/or College/University here which to be honest, isn't the case at all.
On this side of the pond, colleges and universities are all the same thing.
What you're describing would be either Community College or a Junior College (2 years) here. For some, that's the end of the line, and you come out with an Associate's degree or a certificate to the specific field you were studying (usually technical, I think). For others, it's either a way to bring grades up to get into (or a better) college, or to save some money by earning a few credits at a cheaper rate, or while living at home, working a full-time job, raising a child, etc.