There is nothing in the wording that say that a using-directive introduces any names, thus it doesn't introduce any.
(The note is just highlighting this fact; the note in the preceding paragraph points to the change in name lookup that is caused.)

The "introduce name" is mentioned in another place, that is
[basic#pre-5]

Every name is introduced by a declaration, which is a

• declaration, block-declaration, or member-declaration ([dcl.pre], [class.mem]),
• [...]
• using-declarator ([namespace.udecl]),

A using-directive is a declaration that is also a block-declaration. If there is no other place explicitly said such a declaration does not introduce a name, could we say it introduces the name due to [basic#pre-5.1]? Similar, in the section [namespace.udecl], it does not explicitly say that using-declaration introduces a name, however, it does introduce a name, and [basic#pre-5.7] also mention this point.

So, There is nothing in the wording that say that a using-directive introduces any names, thus it doesn't introduce any., which truly is it? In other words, there is nothing in the wording in [namespace.udecl] that says the using-declaration introduces a name, but it indeed does introduce a name. Hence, I think we should explicitly say that a using-directive does not introduce any name in order to exclude it from what says in [basic#pre-5]

What is the specification situation with static_assert? It never introduces a name and also is a member-declaration.

static_assert is a more special case. I just think we should clarify this situation, either from [basic#pre-5] or explicitly say it in each relevant declaration's clause.

Since the note has existed in [namespace.udir#3], turn it to be a normative rule seems do not impact other things, and at least do it would make [namespace.udir] be clear about this point.

Well, saying something in one place and not saying the same thing in another place (e.g. for static_assert) is also confusing. "What's the difference between here and there that would warrant the difference in specification?"

Agreed. [basic#pre-5] is not clear on specifying which concrete declarations that introduce names. It's better to specify them in the respective clause. BTW, "What's the difference between here and there that would warrant the difference in specification?" What does it mean?

If we say X in one place, but don't say X in another place (where it plausibly also applies), we leave confusion whether X does apply to that other place or not.

Yes, it's exactly the status quo of expounding which declarations can introduce names.