One of the points about meditation is about being present, fully experiencing the present moment. By fully experiencing every present moment, you fully experience your life. The opposite would be living perpetually in the future or in the past; not living your life, but continuously preparing to start living it some day.
In your example, the beavers being present and building a dam/collecting fruits are in fact the equivalent of skilled meditators. Dave 'lost in his thoughts' is a person unskilled in meditation, the default situation for a lot of people a lot of the time. Consider how many hours a week people tend to spend distracting themselves, 'lost in their thoughts' - time better spent just sitting and doing nothing, getting bored, and then getting an urge to be creative - like when you were a child.