Effective capacity at 1A down to 2.8V would still have hovered close to 4700mAh, I believe.
Quite likely the chemistry under Samsung 35E, Panasonic/Sanyo GA or LG MJ1 cells inside a bigger cylinder.
Bench Test Results: Vapcell Purple 10A 5000mAh 21700…15A but overrated mAh, runs longer than Samsung
Enjoy!
Cheers