(1) It asks the question “why would they need a warrant if they had the private key”. The answer is obvious: the same reason they’d need a warrant to seize cash from your house even if they had your front door key. Legally, the FBI needs a warrant to seize property in your possession, outside of very narrow exceptions, and “well, we have the technical capability to take it” doesn’t itself qualify for any exception.
(2) It concludes from a warrant and supporting affidavit that explicitly ask the court to permit the FBI to seize BTC to which thet have the private key that...the FBI did not have the private key, but instead was serving the warrant on a “custodial wallet provider” like Coinbase. It it possible the wallet seized was custodial, but there is literally nothing supporting this interpretation of the FBI not actually having the private key ut serving the warrant on a third party rather than seizing it by use of the key in their possession. In fact, every element of that narrative is directly contradicted by the documents pointed to to support it.