We don't have any perfect explanation but maybe Elon musk is increasing his popularity. If I'm not wrong, He is the CEO of Spacex and Tesla. By helping others he is increasing his popularity. Although this year every altcoins will pump, so by helping DOGE coin
Elon Musk is the richest person in the world right now and you think he needs other publicity to get popular 
. Elon is active in social media and this is not the first time he tweets about cryptocurrency and doge coin was his go to coin and you cannot pin point that the price is pumping because of his tweets as he is not asking anyone to pump.