I believe the article is written from a lisp point of view where it interactivity is inspecting and modifying the application itself while it is running. It’s assuming that the software has already been written with no existing concurrency issues, but when a person comes along and does something unexpected and rewrites pose of the application or in the example they gave, modifying a hash map, things break.

They used C as an example because under normal circumstances you compile a binary and don’t modify it at runtime.

I’m not doing to defend it to strongly though, I _think_ that is what they were getting at, but to be honest I found much of it confusing.