A large impact in a shallow ocean area might well in every human dying within a decade. Most immediately. It would also first steam clean the planet, and then set an ice age in motion.
Now I'll grant that this is unlikely in any century, less likely by far, in fact, than that we'll do the same thing to ourselves via war or some other means. (War seems the most likely, but it's not the only contender. An escape from a biological warfare lab is a possibility. I'm not counting natural evolution as "doing it to ourselves", but it's happened to other species. In fact it is currently happening to a large number of amphibian species, some of which have already gone extinct.)
But I do consider asteroid impacts worth worrying about. Not worth obsessing about, however, as they are a bit down the ladder when it comes to humanity exterminators.
I also question his method of assigning proper degree of concern. And the reliability of his assertions. E.g. he claims that only one person has ever been hit by a meteor, but there's no evidence that that's true. He should have said only one person is known to have been hit by a meteor. But how many people in remote areas of the planet could have been hit and the reason for death, or even the fact of death, not officially acknowledged? And clearly nobody could cite an instance before around 1700, as even the existence of meteors was denied. So you need to ask what is the probability of someone being hit by a meteor and the fact being officially recognized. This is a quite different question. He performs the same type of factual manipulation (less obviously) in a few other places.
That said, it's not a major concern while other concerns rate higher. But a species ending event is worthy of particular concern over and above the concern over the individual lives lost, as you also need to consider the future lost, and not just a few personal futures, but all human futures.