Not necessarily. Again, context is extremely important.
As I have defined it for myself - and not for other mods - the lying rule may come into play when two conditions are present:
- A poster accuses another of speaking untruth.
- The accusation also assumes that such is done so knowingly
Once again, however, I don’t feel the need to be locked into things as context is everything.
“You’re a liar” will almost certainly bring about sanction - though not always. Other forms, such as ‘you’re making things up’ as mentioned, may or may not depending on many factors.
Best practice? Don’t accuse others of intentional fabrication. This should not be difficult, I’d imagine.