Your definition of a lie is unusual. Lie is generally defined as intentional deception. If you do not tell people how you are when they do not want to know, you are not lying. Teach him the difference between form ("Hi, how are you?") and substance ("Greetings, fellow earthling, I am happy to not be alone on this planet"), and that replying simply with "Hi" is completely appropriate and is in no way lying.

As for actual lying (intentional deception), you should certainly discourage it in most cases, as there are nearly always better alternatives.