never heard of the orang minyak being armed.
if its only household items being stolen, i think there isn't really a danger. however if u're a lady n u're being terrorised by the orang minyak, then i can safely conclude that it is a danger to u.
they usually strike late in the night. during those times, spore still not tat develop n not as safe as it is. the folklore of the orang minyak is quite widespread esp. among residents in kampung.
it soon died off as more n more residents of kampungs are being relocated to high rise buildings...
as for how the orang minyak becoming a ghost... i've no idea.