Hmm, not really educational articles.
This:

is totally misleading.
Fillfactor value does not allow or disallow SQL Server to fill up the pages in any particular way.
It will always try to fill pages in the most effective way (well, according to its internal algorythms).

This

is pretty much rubbish.
On the server level there is a default value of fill factor. Which may not match any of actuall fill factor values for any index anywhere accross the server.
And fill factor on a table level is simply a nonsense.

Don't put too much faith in those articles.