Earlier quoted context omitted.
The recruiter was in idiot but not to consider c# dev for Java job is quite silly too.
C# and Java the language are similar enough; the ecosystems are very different. A C# developer would mostly be expecting to develop Windows programs or possibly Windows server / IIS applications. A Java developer could be working on all kinds of different things.
Also, rejecting someone because they can't rote memorize ecosystem specific incantations is... a pretty big red flag.