Why does Windows think my .exe. is a .dll?

I compiled a simple C++ program with the following link line (I'm using mingw):

c++ -o fix.exe mainfix.o FixIncludes.o ..\util\lib\util.a 

The link occurs with no error.

file fix.exe returns:

fix.exe; PE32+ executable for MS Windows (console) Mono/.Net assembly

But when I try to run it (it takes a directory name):

./fix .

I get the error

The procedure entry point ZNKSt25_codecvt_utf8_baseiwE10d0_unshfitERiPcS2_RS2 could not be located in the dynamic link library fix.exe.

Why does Windows think my .exe is a dynamic link library?