Does anyone know what this dark red colored discharge is from this grilled chicken?
@pb2q is right, it's blood. This happens during processing. When the meat isn't allowed to bleed (i.e.; drain blood) long enough, then some of the blood remains in the muscle structure and cooks along with the chicken. It might look odd, but it's not a concern as far as eating it is concerned. It won't "hurt you".
If it bothers you (as it might for some people), just remind yourself not to buy that brand of chicken again. If one bird from this company was rushed during processing, there's a reasonable chance that they always "rush the process". Easiest solution might be to just switch brands... but please, don't thrown out the Tandori Chicken. I bet it's... delish!