I agree with the other mother's sentiment, but it is indeed a harsh way to express it. I've never done Santa, was never brought up with it and find some families can be a bit weirdly over the top, but I wouldn't go around telling other people that they were 'lying' to their children. I'd happily say here that it's all a myth/bunch of fibs though. Mostly I do the equivalent of 'oh yes' and move on, or I might say 'we don't do FC' and leave it at that.
Otherwise I suspect I'm probably quite like that other mum because I like giving explanations of how the world works, and when my children were asking 'why' I wanted to share my knowledge (such that I had!). I would have felt very odd giving them a more fluffy response because that's not the sort of person I am. My children had a very healthy sense of fantasy and we read lots of fantastical books, but I never wanted them to think (for example) that the Gruffalo was real. They had imaginary friends and spent a huge amount of time playing 'lets pretend' and we have created some fairly silly family myths from time to time. But they have known perfectly well that they were pretend because they were a part of creating them.
To me Santa doesn't fit into the family magic category because it's mainly a commercial creation. Yes there are some interesting root myths, but it's all a bit of an industry now, and it' not one I ever felt a need to be a part of. But then I didn't growing up knowing anyone who made a big deal of Santa, and I've never in any way felt I missed out on my parents not doing it (and yes of course they loved us, very much, and we had fantastic Christmases and still do). Plus I feel a bit embarrassed watching some other parents tying themselves into knots trying to keep their skeptical child in line with the belief, and I really don't understand why they think it is so very important.
I like your solution PrettyCandles, one of the reasons I dislike the FC/Santa stuff is that to me it seems very wrong to have presents with no reciprocation or thank yous. I really do believe that the giving of gifts should be at least as important as the getting, if not more.