Average lifespan is calculated differently for non-humans. Humans count actual average amount of time lived including infant mortality, while animals are typically only calculated from after a certain amount of time has passed (sometimes only counting adults).

Otherwise you would get super skewed results for animals like octopodes (other plurals include octopuses or octopi) which have tens of thousands or even hundreds of thousands of babies at once, of which some lucky species have a survival rate of 1% before adulthood. This would make the average lifespan of an octopus anywhere from a couple days to a few hours.

It is strange and somewhat inconsistent, and this causes the numbers to be Skewed for animals like zebras. But I get why they want to avoid numbers that would be utterly useless for some species.