It looks like the worst time to hold any alts at the moment , every bitcoin movement up or down creates a sellof for altcoins including monero.
I don't think it's causing a 'sell off'. BTC is just out performing everything right now. But it will pass. Those buyers will run out of bullets and will be forced to hedge in alts sooner or later.
I got me an alt that I'm bagholding that I wish to god it would pump now! I feel dirty holding this. Lmao.