Not necessary that they died in siddhasana!! It would be wonderful if they really did !! However, There is a custom in India to bury people in a seated posture. It is more likely that it is so. It is interesting that this was found in Romania and not India !! It would be wonderful to know more about this.
That's why Sadhguru adds, if you manifest something, only then we can talk about it.. Sadhguru can clearly see that that was a Yogi died in cross-legged posture..