How can this 10-bit ADC getting 16-bit performance?

[Bootalito]

I bought this panel meter a while ago: https://www.amazon.com/gp/product/B00BYOL4JM/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

I just took it out and started messing with it to see if I wanted to use it in a project, and its accurate from 0.000 - 30.000 down to the 1LSB when compared to my 500,000 count brymen BM867s  It has an ST micro STM8S003F3 Datasheet from Mouser.com which only has a 10-bit ADC.  How is it measuring the difference between 30.000 and 30.001 which should only be possible with a 16-bit+ ADC?!

[Kleinstein]

There is an external ADC in a SOT23-6 package, likely an MCP3421 - this is an 18 Bit ADC with internal reference.

[Neganur]

those modules are way cool for how cheap they are.
Even though the last digit is a bit iffy, I'd say it's easily within +/-100uV