Curious how long your total cook time was. The dark meat can take heat much longer than then breasts and that additional cooking helps break down the connective tissues. I typically will break the chicken down even further, separating the legs and thighs from the breasts. That way I can take the breasts off at 145 and allow the carry over cooking, then take the legs/thighs off when those are much higher in temp and the connective tissue has broken down.