It does mean doubts. It's a dictionary that intends to solve all kind of doubts that one may have when it comes to using Spanish. It was published by the Real Academia Española.
You're wrong there! This is the first one, not published just by the RAE, but a collective work from 22 Academies from different countries, including Argentina, Mexico, and even USA. This is the written consensus used by all this countries when it comes to correct orthography.
And there is a good reason for it too. The comma represent a short pause, and an ascending tone. This intonation is to be expected, since we haven quite finished our sentence yet; that's why we put commas in the middle of a sentence in both languages. But in speaking, when we say "Hello", we normally use a descending intonation, and then leave a fairly long pause before continuing with whatever we want to say. A comma is exactly normally used for exactly the opposite of what we try to say, which makes me wonder why using a comma here. The full stop (period) and the colon represent in both languages a long pause and a descending intonation, which is, interestingly, exactly what we'd need after "Hello".
Logical or not, each language has its own convention, it the colon has been the Spanish convention for many centuries; the fashion of starting using the comma after "Hola" is probably a result of being in contact with English speakers, writing to them, translating their letters, and above all... because in Internet all pages and fora use the comma for letters, and we hardly get the chance to see letters written by educated Spanish speakers. My parents and grandparents, who speak no English whatsoever, were shocked when I told them about the comma.