I assume you are referring to the part where article says that (hall effect sensor) "output being used to trigger MOSFETs". I have no idea where that came from, but in the schemeatics and code I looked at hall effect output was read using ADC like you would expect. Otherwise how else would you change the actuation point? You could digitise it by comparing it against adjustment pot with a discrete comparator IC, but that seems like 80% of hassle with 20% of functionality. Sample keypad in the linked repository doesn't do that. Either I am looking at different repository or Arstechnica writer blindly copied from the hackaday article, and hackaday writer was half asleep while reading schematic so wrote complete nonsense.