Probably just an app they made that scraped every of the 3100+ counties websites, just did it maybe faster than the gov or consolidation websites which are cached and prob badly written. His was prob python or rust or something fast. Could even be something writtern badly and fast and simple like js and an off the shelf github html scraping kit (many exist) and just got the numbers and collated them in realtime.

And then add to that some logic that says basically 'here's historically the number of voters per county...here's which are registered this year sans those removed from voter rolls' and from that you get the percentage to total, and using this calculated that at a certain point, Trump won the popular vote BEYOND what they would reasonably be capable of overcoming (without ballot drops of fake ballot frauds), and so they'd conclude he wins the electoral votes for those states that have winner take all (which is all of them except for maine and nebraska iirc)

and once you get close to 270 and they're so badly behind, you know you're goint to get there before they do, and then it's over, even if they ballot dropped

This is also how we knew we won the senate and house before we knew we won the senate and house. The Rs were winning those undecided yet, but were so far ahead that even with the remaining %, if the trend (ratio of D to R) continued, they would lose, absent a statistically outlying uptick in only one sided ballots (meaning fake / steal)