Shebang line and ruby

Hi!
                  I am learning Ruby and I was using python earlier.
    I was trying out small scripts ( cut and pasted from ruby docs )
    and in one script I added shebang line invloking python instead
    of ruby by mistake ( I use a bunch of vim 'abbreviations ' in my
    .vimrc to add the lines for perl , python ,sh. etc). When I ran
    " ruby file.rb" , ruby exec'd python !
    
     Had I made the file executable and run it as "./file.rb" this
     would have been understandable -- shell calling python
     but ruby using the shebang line ?
    
    I thought only the shell is supposed to use the shebang line.

    I run ruby 1.8.2 on Debian 3.1
    I also tried it on ruby 1.8.2 on Redhat 7.3 with the same results.