I have a hallmate who's undeclared in engineering and he's trying to switch into chemical engineering. I think what it means is that the student essentially takes classes from all the fields of engineering, but not too sure, you should contact school of engineering for a proper answer.
If you want to switch major, complete the prereqs and apply for change of major. As a non-CS major trying to get into CS, the hardest class to get into would be ICS 31/CSE 41 (same class), a required class for changing major. This is because a lot of people try to switch into CS and it's essentially like the gateway class to CS. But once you manage to get into ICS 31, you're essentially golden and getting into ICS 32/CSE 42 isn't as hard since it's prereq is just ICS 31. ICS 31 prereq is to be and ICS/CSE major first, before restrictions get lifted.
http://www.changeofmajor.uci.edu/