Garuda Purana describes the method of breaking brahmarandhra.
56-50. Whether half or wholly burnt, his skull should be split open,
in the case of householders with a piece of wood, in that of ascetics
with a cocoanut.
His son, so that he may attain the world of the forefathers, having
split open the brahmarandra should make an oblation of ...
Siddhis (Sanskrit: सिद्धि siddhi; fulfillment, accomplishment) are spiritual, paranormal, supernatural, or otherwise magical powers, abilities, and attainments that are the products of spiritual advancement through sādhanās such as meditation and yoga.
The King in question might have obtained the siddhi - Prāpti:, ability to be anywhere at will.
Menstruation is considered as ashaucha (ritual impurity) that is why it is advised not to touch a menstruating woman.Some verses from scriptures which clearly say menstruation is a ritual impurity, and this impurity is temporary only. It helps woman to realise there impurity or sins.
Vasishta Dharma Sutra V. 4-5 “For month by month the menstrual excretion ...