Nope, I visited his twitter account and I don't see he shilling ADA so it's a fake news. Maybe you really saw a post that he will invest ADA but a fake Elon Musk account, you better double check the account just to be sure if he is real. If Elon Musk shilling ADA it's another mooning for sure.
Maybe that news is just made as bait. Having a big man holding such coin will make other investors to see opportunity on the same. That is big chance that the coin will reach a good price if it is possible that he invest on the coin since Elon Musk is popular all over the world.