The prometheus chat just shows Prometheus saying Dan Metcalf was  "hal dev"...what ever that means.

It could mean he was a dev who was looking at HAL's code.
This is the only interpretation that makes any sense, as we know that many coins had asked dan to look over their codes.
Why would they do this? Because they knew Dan was respected as a developer.

It makes no sense in the light of all the other things we know to twist this snippet to make out that Dan Metcalf was HAL"s developer.