Even my grandma can explain Bitcoin quite well and you consider the possibility that Elon Musk didn't do enough research (best scientists in the world work for hm) to understand Bitcoin but gamble a couple billion dollars on it anyway. 
Are you serious about the grandma thingy or its just an exaggeration of the fact because, I'm out here wondering what era us your grandma from to have such claimed knowledge of bitcoin. Well let's not get too fancy. About Elon Musk having the best scientists, of cause he does or can but still, could get financial bad advice. You know, it's more like a scale to balance kind of thing. He checks his company and what it stands for (being the promoter of renewable energy sources) and here he is representing a field that consumes a significant amount of fossil energy sources.
I guess he only came to the realisation of this complications after that tweet of Tesla accepting bitcoin as it came down with some negative responses from critics. For one, it was just an investment and now, its about the idea he came with.
Other way to look at it is, it being a conspiracy to buy the dump and also assist the growth of Dogecoin. No doubt his got a lot accumulated already.