Fireplace Mantle backboard? Mounting Flatscreen?

With my trusty studfinder I located a 2x10 mounted flat against the drywall about 4-5 feet off the floor about the fireplace in this condo. Studs were 16 in on center above and below but then there is this sandwich of a 2x10, 1/2" MSB and another 2x10. I ended up mounting the flat screen above into the studs but really wanted to go where this goofy 2x10 is. Any idea of its purpose and stability for a 110 pound load?
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