Not an indicator, it just happens that it may be a good indicator for some assets for some time. Bitcoin is a currency and hopefully you will engage yourself appreciating that it's widely use as a medium of exchange. It is for long term, you do not have to tune up for its movement every single day and rant here because it is given that it is volatile.
How he thought that Bitcoin was just an indicator, really? Just like you said, it can serve as an indicator for some cryptocurrencies, but it is not even all the crypto currencies in the market that follows the price of Bitcoin just like the people would always say it.
There are thousands of cryptocurrencies in the market these days, a majority of them don’t even move the same direction, they move totally different. Even these days I no longer say that when Bitcoin goes up that altcoins follows it, because I know that wouldn’t be the case, there are many these days, and they wouldn’t be doing the same thing that Bitcoin is doing. And moreover that is what we really want, we need that diversity in the market, and not all the coins doing the same thing all the time.