There are 2 groups of people, group A and group B. The groups were NOT assigned randomly and are not the same size. 

It is true that group B has a higher rate of success than group A, but this was not the result of an experiment, it was noticed during after-the-fact analysis. 

People I work with are using the words "control group" and "test group" to refer to groups A and B, but to me this seems inappropriate because they were not designed prior to analysis. Do others agree with me or is it okay to blur these lines a bit?