I don't think Elon Musk is too serious in saying that Doge is a good coin, it looks like he's just kidding, but a lot of people take it too seriously, so many people buy Dogecoin and take the opportunity, that's why a famous person like Elon Musk has such a big impact in the crypto world
I don't think Elon Musk tweets about dogecoin with the intention of joking. Rather, he promotes it so that more and more people will buy it. Although he is not the first person to promote dogecoin, some well-known TikTok celebrities have done this before.
We shouldn't buy any coin at the recommendation of such a celebrity.