Yes I agree, however it could also conclude that someone is holding out; as in not wanting to give out too much information. In many instances such as these the information given could be detrimental. Therefore the person who was asked a question may have a need to protect themselves.

This phrase is used when someone says something, but you don't think it's too special/important, or that the information is not sufficient. The context is needed for the exact meaning.

We often use this in a joking way. For example, let's say that there is a joke in your region that the residents of a particular town are stupid. If someone mentions that a person got top marks in his exams in that town's college, you might comment 'That's not saying much'. This means that it isn't really a particularly significant achievement, considering the supposed average intelligence of the people in that town.