Their allegations are not entirely off base. The Coinbase BCH launch was a complete disaster. The BCH price pumped for days on other exchanges leading up to the announcement. See here for some more information:

https://motherboard.vice.com/en_us/article/pam4xn/coinbase-i...

In addition, they opened up trading on GDAX, but waited to open up buys and sells on Coinbase until Roger Ver’s segment on CNBC Fast Money (right when the price was at its highest).

That said, I do not think Coinbase should pay someone back for making a poor decision with their money. People like to deflect their own mistakes instead of taking responsibility. Coinbase didn’t make this person buy BCH at $5,000.