Judging by the code, Companion Drones (https://mods.factorio.com/mod/Companion_Drones, the successor to Construction Drones) specifically look for the "chemical" fuel category when creating a list of fuels that the drones can use.
This means that fuels that have only the K2 fuel category "vehicle-fuel", like Biofuel or Processed Fuel from AAI Industry can't be used by Companion Drones.
I'm not sure if it should be considered as a K2 bug, or a Companion Drones one, so let me know if I should file this for Companion Drones instead.
K2 version: 1.0.23, Factorio version: 1.1.27, K2 was active at the start of the game.
