Elon musk is really shilling and hyping dogecoin to attract invest which are mostly newbie and small time investors which tend to get FOMOed. And that id true that he bought a very large and enormous amount of dogecoin which mean he is one of those big whales in dogecoin so when he decided to sell it dogecoin coin will definitely be back to where it started.
I did my own research and so far, I am not getting anything about Elon giving any mention of any other cryptocurrencies other than Bitcoin and Dogecoin. I am not able to find anything, not even a tweet or a news article that would suggest that he mentioned any other cryptocurrencies other than the one he already mentioned. I think he is really serious only on those two coins and there is nothing else he is serious in getting.