I wonder if the article got a bit confused and it has two 4,000mah bats that equal 8,000.
16,000 is a huge amount of space to take up in a device that size. Plus, it says the 5" would be good for 7 hours. That really wouldn't be very good if it were 16,000mah.
They've been getting more powerful - and power hungry - each generation. The original Pi had a max load power usage of less than two watts. The Pi 4 gets up to 7W, and now the Pi 5 can peak to 12.
Ehh, neat idea, but I already carry a laptop and a phone. Today's laptops have some serious runtime on battery. Plus I tend to use the smallest laptop I can, like the Lenovo X Series (still have my X61, really like that form factor).
I do use an iPad around the house to play a few games. So it's not like I don't already have the use case at home anyway. Maybe if I didn't have the iPad this would work for that.