Notice the .mdl.r2009b file in the directory? Rename that so it does not have a .r2009b file extension, just the .mdl file extension.
Notice how you have a .slx file with the same basic name? That could only have been created by running Simulink R2012a or later, as .slx files had not been introduced until then. When the model was opened under R2012a or later and when who-ever did that agreed to the prompt to save it as SLX, the .mdl version was renamed.