If I was a very large buyer who wanted to take a substantial position in BTC without raising the price too much one possible strategy would be to systemically and randomly pump various alt coins to intice Bitcoin holders to sell via FOMO.
I don't have any evidence this is occurring and I do not trade but when the market behaves strangely one must consider strange explanations.
That's sound reasoning that hadn't actually occurred to me before, but you'd have to be very friendly with the alt exchanges and trust them enough not to crater. If I was a megabuyer I wouldn't have enough faith in them. Poloniex is creaking badly.