I'm surprised the copy editor was more comfortable using git than using a web-based review tool to leave comments, especially given that she was reviewing a Go book and didn't seem to know what Go was.
How does that even happen? It seems bizarre that Manning had this copy editor at all.
I recently had a negative experience with Manning. I sent them an email saying that I'm in the process of writing a book, and I'm self-publishing it, but I was curious about the possibility of applying to Manning for a second edition. I asked whether they accept second editions after a self-published first edition and what document formats they accept.
I got back a form letter telling me that they'd rejected my proposal. When I followed up and said I didn't send a proposal but was asking preliminary questions, they told me that they understood I hadn't sent a proposal, but they were going off of the table of contents on my book's website. I guess they decided to pre-emptively reject me?
They also only said Google Docs as a document format, but based on this blog post, clearly they accept AsciiDoc.