Yep, traditional parenting norms are completely inconsistent! Well, they aren't, but it depends which lens you're looking at parenting through. If you're looking at it through the more modern lens of parenting being teaching children about the world/supporting developmental skills, then it's inconsistent. If you're looking at it through the more traditional lens of using a hierarchical structure to get children to behave manageably, while they're young enough not to understand what is dangerous or inconvenient to others, then it works fine because the rule is children don't lie to adults in order to benefit themselves - it's a respect thing which goes one way by design.
Firstly there's no real black and white "lying is bad" - we do acceptable lying in many contexts and it's considered absolutely fine/preferable to telling the truth. For example "Do you like my new dress?" (when you think it's hideous) "Thank you Grandma, what a lovely present!" (when you hate it).
Secondly stories/pretending are a form of lying (you can differentiate it, but essentially to many young children, and even more so for children with a condition like ASD, it's still fantasy vs reality). You can see sometimes in ASD kids' recollections of school that taking something too seriously can be seen as impertinence when really they are just confused because they think that a teacher would always tell the absolute truth, and not use stories/metaphor/etc to explain something.
Personally I don't go out of my way to "preserve the santa story" - we just treat it as a festive story really and don't take it too seriously. But I am also not particularly arsed if my kids lie because it's really no indicator of moral decay like people used to think. Most of the time it's a completely normal developmental stage, and it's our job to help them understand when it's appropriate to lie and when it's not, not to come down really hard on certain forms of lying and then also punish them for not lying at other times - it's confusing.
IME people who "hate lying" are the worst liars themselves! DH gets really worked up about it yet I've heard him tell some absolute corkers to his parents and even bosses/colleagues before! I rarely ever lie, I have a terrible memory and it makes me anxious, but I am not especially bothered by the kids lying if I can see why they were doing it, I'd rather address that.