The first point is of interest to me, too, relative newbie here though I am, and I offer my opinion that it’s quite different from accusing someone of lying. The prohibition against accusing someone of lying or being a liar is something that I think most of us can live with because it’s unnecessarily insulting and hostile. But when we start outlawing anything that can even remotely be considered possibly synonymous, then IMHO we start to seriously impair the ability to communicate on this board. Which is my answer to the basic question in the OP – it may or may not be equivalent to an accusation of lying depending on context, and the mods can make that call, but we don’t need any more rules that impair the ability to communicate basic ideas.
Getting back to that first point again, when you say that someone “just made it up” that implies to me that the poster made a statement that he might very well believe to be true and might even be true, but for which he has not provided any citation. One would typically be expressing doubt that such cite could ever be provided, not necessarily because the statement is false, but perhaps because it’s a value judgment not amenable to such validation. All of that is nicely summed up by saying “you just made it up”, basically synonymous with “you stated as fact something which clearly can never be substantiated” which is distinctly different from “you are a lying jerk”. So I’ll say again: it’s fine to have rules that promote civil discourse, but not rules so far gone that we can’t properly communicate, and in particular, that impairs the ability to call out complete bullshit when we see it.