Period changes and Ethereum is beginning to perform independently from Bitcoin this period of time, last week we saw how the price of Ethereum keep soaring untill it hit another all time high, at that point Bitcoin was in the opposite direction doing a decline in price, this move shown a significant change of trends and for that reason we can now point Ethereum to be self sustaining in terms of price movement unlike in the last where everything depends on the Bitcoin market trends to determine altcoins market.
A week of diverging price action isn't sufficient to call a long trend change, thats a classic example of recency bias. Look at both charts and compare them side by side if you havent already.
Keep in mind the entire crypto market, including Ethereum, is still largely connected to Bitcoin and follows Bitcoin. I mean, if Bitcoin experiences a massive crash, do you think Ethereum would not go down? No! It would get dragged along with every other alt coin.