It would be similar to a priest hiring a secretary for the parish and asking if she was a Catholic and the interviewee responded by saying: "I'm a Christian". Would anyone be surprised if she were turned down for the job?
The simple fact of the matter is that Mr. Clark is suing the Salvation Army because they didn't like his parochial response to a broad non-denominational question. He failed the interview and is now blaming the interviewer. In light of his litigious attitude, I would have to question whether or not he would have been telling the truth if he had said yes.
It's not remotely similar. "Catholic" is more specific than "Christian". Mr. Clark's situation is the reverse.
That having been said, he shouldn't have been working for a Protestant church in the first place.