That is exactly what it is
I had my towel rack fall off also. Lowes carries 2,3&4 foot long oak strips that come in different widths and different thicknesses. I purchased a piece 24" wide by 1/4" thick by 2 1/2 " wide and mounted that to the door with glue and a few staple with the air nailer, then mounted the towel rack to that. No problem now
My two sliding doors have web straps with snaps to hold them open when traveling. Frank