Their comment is putting everyone in two buckets, 1 that sits around and watches TV when they get home from work, and 1 that works on personal development in their free time.
What they want to use that personal development is up to them. They could use it to start a non-profit, or learn a new hobby or learn a new skill. But... sitting around watching TV until bed certainly isn't ambitious.
But here's the thing: the "watch TV/self-development" dichotomy exists and keeps existing at every level of actual achievement. There are people who think that lawyers, doctors, and software engineers are underachievers for not becoming CEOs, after all. Lawyers, doctors, and software engineers tend to think people working old-fashioned 9-5 jobs instead of high-level professions are underachievers. People in old-fashioned 9-5 jobs think part-timers are underachievers.
And in the other direction, there are people who think that anyone who merely runs a business and doesn't build an international business conglomerate is an underachiever. There are people who think that running an international business conglomerate instead of a world empire makes you an underachiever.
There's at least a few people who think that running a worldwide empire makes you an underachiever, because you should be trying to become a god!
Sometimes all you have is an impulse to go in a direction, but not a destination. Those are the impulses to go out for, when no actual destination will sate the impulse.
There are two kinds of people in this world:
1) Those who hit some ceiling and actually achieve contentment.
2) All-consuming psychopaths who love looking down on everyone else for their lack of ambition.
I was born the second, but I sure as hell don't have to stay that way.
Also, side comment: some of us don't want to be employer-capitalists. We like doing things for their own sakes, not so that we can turn every activity in life into a money pump. As such, by your notions, we simply don't have ambition.
By my notions, the default ambition you remark upon, the urge to become a wealthy, high-status leader of some sort, is indeed psychopathic. Why should I want to become a capitalist, military general, or statesman? I could stand being an activist leader, but I don't think I'd be much good at it.
On the other hand, if you ask me if I wanted to, for instance, destroy all existing social relations and have a socialist revolution, I happily say "yes". But somehow Revolution is simply not as ambitious as "become an employer", or as "become a research professor" (which is actually harder than becoming an employer).
Which, again, makes it sound to me like your definition of "ambition" is "a rise in wealth and social status" rather than any coherent notion of actual achievement.