When spark lose signal with RC, RTH is activated. In my case is activated and some seconds later it say something like "RTH error". So I trigger RTH button on RC and then spark fly to me.. So question is: if they are disconnected( RC<>Spark), how then the spark suddenly can receive RTH signal from Rc to come home(when its trigerred manual)??

Probably it regained connectivity

SPARK never loses connectivity with RC. If it does , the firmware inside SPARK will initiate the fail safe program and return as per current RTH location address.
So dont worry, there are systems in place..

Hi, there. More info about RTH, please read our user manual carefully. Thanks for your attention.