You shouldn't think that this rule gives complete information on the use of "say" and "tell" in English.
"Say" means pretty much the same as "utter", only you can utter any kind of sound, but you usually say words. When you ask someone a question, you are saying something. When you tell somebody about your day, you are also saying something. We often say things to somebody. But sometimes the things we say don't have any particular addressee. When I bang my head against a piece of furniture and say "ouch" or "damn", I'm not saying it to anyone.
When you tell someone something, it is usually a piece of information. You can tell me your age, a lie or what happened to your sister a week ago. When you ask me a question, you're not telling me anything (but you're probably expecting me to tell you something).