.par2 files are simply an efficient way of repairing any kind of file that gets posted to Usenet and might have its parts incomplete.
alt.binz can automatically check which and how many .par2 (parity) files you might need to complete the set, download them and repair the .rar files for you, and then extract the contents of the .rar files to disk and then delete them, leaving you with just the contents of the .rars - the .iso.
The
.par2 files repair the
.rar and then the .rar archive is extracted.
It hasn't deleted the .par2 files because you don't have the option checked to do so after repair, so they get left on your hard drive.
If you have the program, Winrar can also open .iso files as if they were a .rar or .zip archive - this is what your Google result referred to. It automatically sets itself to have .iso files identified with it.
However, alt.binz has done its job for you, so now you can burn the iso and play.