It cycles through the rows in column 1 first. So if your data is called a and your mean vector is called m it would do a[1,1]/m then a[2,1]/m then a[3,1]/m then a[4,1]/m then recycle the mean vector to give a[5,1]/m.
You could use the sweep function to do what you want.
> m <-...
Ackkkktulllyyyyy... It is loaded from a file. Typically lazy loaded and you don't need to specify the absolute path for the data file but... Yeah it's loaded from a file that gets installed when you install the package.