Disclaimer: I've never studied a patch like you did.
The "Only in" looks like output from "diff -r" (
man diff). It does a r
ecursive diff across two directories, say A and B. If both contain a plain file with the same name, say c, diff shows differences between A/c and B/c. If a file d only exists in one of the directories, diff reports, e.g., "Only in A: d".
A basic patch is typically produced by "diff" (i.e., it's saved output from "diff") and applied by "patch". This is very basic, and I don't think it would handle addition of new files (one case where you'd get "Only in") properly. I'm sure that Linux patches have much better ways for applying them, both more sophisticated and easier to use.