Nope, it's not. It is because of the news about what happened to Mt. Gox, the news that google and some major social media site will be banning cryptocurrency and ICO advertisement due to a lot of scam ICO had been advertising their project using either google or social media sites. I really think that it affected the market demand greatly.
I think Mt. Gox is also not the real reason for this one because recently in the news statement they have already mentioned that gox. sell is not responsible for the current drop in the market. But who knows what they are trying to cover up with such news. May be billions of dollars that they are holding?
One thing is sure that altcoins are not the reason as they have their own investment portfolio and most of the investors keep both the investment as separate one. If you really think its altcoins then just ask yourself one more question, if bitcoin is down then why altcoins are down at the same time? Isn't that is a thing which we must analyse before our conclusions.