Joules, Amps and Portable Jump Starters

I recently purchased one of those portable jump starters. A Noco GB40. I took it apart to see what it's all about and am having trouble making sense of some of the specs/claims.
Does anyone know how you would calculate the Joules and the amps they claim?
From my research, there are 3x 3.7v 2150mah 60C lithium batteries in here. So a lot less than others, yet some others on the market claim only 400amp with similar sized batteries.
Is there any way to test the 1000amp claim on these? Does that number even seem realistic?
Is there any way to test the Joules they claim (7000joules for 3s)?

Thank you for the help. Just trying to see if this is marketing hype or may actually be what it claims.

I would assume that it is marketed like some audio amplifiers in that it will produce that power WLS kind of scenario.

WLS (When Lightening Strikes)

I have had to replace an ANL200 fuse that is soldered in a case on a Matco box similar to this one.