This is so timely to me, because when I got married a couple of months ago and was changing my name everywhere, every place I called they would automatically say "Congratulations!" And because I have kind of a twisted sense of humor I would think (but never say, don't worry!) "How do they know this is a good thing? Maybe it's a shotgun wedding! Maybe my boyfriend lost me in a bet! Maybe my father traded me for meth money!" Thankfully, it's none of those things. But because every single credit card/bank card/document/what-have-you had a completely different method for changing my name, I would typically start these calls with "So I just got married, and I need to change the name on my card...?" at which point I would get the "Congratulations!" But in a couple of instances, I just started with "I need to change my name" and I still got a congrats. I found that super amusing - what if it was a divorce, or something else? (Running from the law, maybe?)
Anyway, I certainly didn't care that someone congratulated me, but I wouldn't have taken offense if they hadn't. In fact, I would have found that more normal. In short: this client was a nutter.