Curious that Groovy case can match values that are not equal to the candidate

[KARR, DAVID]

Reading REGINA, I find this detail of Groovy semantics very curious:
----------------------
def myList = ['a', 'b', 'c']
switch ('c') {
case myList: assert true;break;
default: assert false;break;
}
--------------

In all the languages I'm aware of with some sort of "switch/case" construct, 
you can always assume that if the "case" matches, then the "case" value "is 
equal to" the switch candidate.  This is the first time I've seen this not be 
the case.

I certainly understand what Groovy is doing here, and I appreciate the power of 
it, it's just a bit surprising.