How exactly do altcoins gain value? There are so many altcoins out there and honestly you can see connection among these in terms of the drop and rise of price.
No, altcoins are not from Bitcoin per se. However, their concept is from Bitcoin. Bitcoin is the pioneer cryptocurrency in the market, and in every market, there should be a pioneer asset where other assets would pattern their production from. Although they are supported by different technologies and are virtually different from one another, they also have similarities as currencies, investment and trade mediums, and hold-able assets that can be encased in the future.
My opinion on this is that altcoins were made and mostly patterned with bitcoin. In relation to the market movement trend, I would say that BTC and altoins were merely correlated with each other as what we had seen in the previous days where price of BTC had dropped big and same with the altcoins.
However, there were few altcoins that hasn't much affected during the market crush mainly because of it's good performance and reputation just like Ethereum coin.