Well, there are British people – as there are everywhere – that don’t seem to know anything. Just watch any of the low-brow quiz shows. At the risk of sounding patronising, a couple of people is not a representative sample.
But yes, is the answer. In as much as British school pupils do any history these days (and they don’t do much, see my other answers on this topic), the British Empire is certainly a topic that is covered, and it is presented mostly as “a bad thing”, especially as slavery is often covered at much the same time.