If they were dry AND not falling apart, I'd guess undercooked.
What crimsson said about grate temps being lower than a dome mounted thermometer also applies. Looking at your pic, I see the probe inbetween the ribs on the grate. I wonder if it was touching the meat or grate.
Try bend, poke, or bone pull test for determining when ribs are done.
Modded Brinkmann Gourmet. Basic UDS. Rescued 22.5" OTS. SJS Mini-WSM. Stubbs. B&B Oak Lump.
Cannondale 2009 F8 (for burning off all the great BBQ)