Well, on the FauxPilot side I did do the initial implementation personally (over the course of a few weeks this summer) – but of course I'm building on the work the Salesforce team put into training the CodeGen models, and the work NVIDIA did in creating the FasterTransformer inference library and Triton inference server that FauxPilot uses.
I don't know how things are organized within GitLab, but it's pretty plausible to me that one engineer could put together the completion portion of the VSCode extension – you can see the code here: https://gitlab.com/gitlab-org/gitlab-vscode-extension/-/blob...
Fred has also been providing pull requests to improve FauxPilot, which I very much appreciate! :)