If you want to diversify, you must choose non-correlated assets. Non-correlated coins do exist. Just look at the article's 2017 chart. BCH was not correlated with BTC, so diversifying into BCH was a good choice. This year, however, you will need to find other coins.
i disagree.
altcoins in the long run, they all act the same meaning they go down whenever bitcoin is active. and BCH has not been an exception to this rule either. the difference is that BCH has been new, controversial and advertised to death in the short time it existed so it might have acted a little differently from other altcoins.
but for instance when bitcoin drop began in December, BCH drop also started with a little delay since it was on a pumping spree with also a delay but the drop happened with the same process.
of course in short term (less than a couple of days) there is always exceptions because pumps happen.