How does this exactly work?
I don't know what I would expect to come from there, but definitely not
_ is a space.
\csname<name of cs>\endcsname would expand in one expansion to the control sequence
<name of cs>. Now, I thought
\string would print the next token, and, if it's a control sequence print
\escapechar<name of cs>, but I'm getting something different. Where's the problem?