With this comments he means that cryptos are out of his investing universe because they do not have a balance, cash-flow, taxes, shares, etc... that his team can analyse. It does not mean that they are worthless.
that quote has two parts, and what you are focusing on is the second part ("not producing anything") but the first part which you ignored is the stupidest statement that anybody can make.
bitcoin does have value since it is providing a utility and it doesn't have to produce anything to have that value. and when he says it has no value he is saying it is worthless.
The definition of "value" for WB is not what you would usually understand as value in an economic context, rather a concept related to the value of companies - hence this statement that may seem wrong to people who are not familiar with his philosophy.
Just for the shake of the argument, it is the bitcoin network (miners, users, exchanges,...) that actually provide economic value. Bitcoins are just an electronic record on a database replicated in many nodes. I recently had a look at Adam Smith´s works regarding that wealth is a nations labour and ability to produce, not their stores of precious metals. Looks like it could be applied here.
It's actually GOOD that Warren Buffett has missed a golden opportunity to invest in one of the largest asset price moves of the century. How long must the network exist before these people accept Bitcoin as an asset, and as a protocol?
There is one rule that WB tries to follow strictly: Avoid any chance of permanent loss of capital. This obviously means that many opportunities will be lost, but also that risk is carefully minimised.
In many ways Warren Buffett was right, bitcoin is a rat poison. The rats are those corrupt powers that had the centralized world by the balls all these years and have always been feeling threatened by anything decentralized that could take that power out of their hands and give it back to the individuals that deserve it.
That said buffet is legacy so he doesn't need to care his successors will for him
WB was absolutely unhappy with the Fed giveaways of helicopter money. As he said famously, when the tide is low, you can see who is not wearing the swimsuit. However the Fed has made sure that the tide was never low and Warren could not use the crisis to hunt any Elephant with his humongous cash reserves.
Tip for the future: Now all companies consider safe to take risks beyond reason - AKA swimming naked.