I'm not sure how you've interpreted the phrase "almost indefinite" as meaning "incredibly short lifespan" but it undoubtedly means they have a long but unknown lifespan.

Because of indefinite's definition. It doesn't mean long or short it means unknown. Which is pretty much worthless.

It's probably a typo and they meant to write "almost infinite". Which actually makes sense.

Perhaps misread as "indeterminate" ?