We have to stop taking Elon Musk seriously and sometimes ignore his tweets. He does such gimmiks to get attention of his followers and make them ponder. Or at times it is done intentionally to market his product or mission , for example consider Tesla's launch of MUV where he shattered the glass. It was for sure played well and was a way to male things viral. I am sure after all these years of interest in space exploration that Mars is indeed not flat and Earth like.