the context for that comment is that handshake took a snapshot of the icann namespace. so any names icann adds or changes after the fact will conflict with the HNS namespace.
As to being adversarial... ICANN was allocated 1.2% of the total HNS supply, and all existing TLD owners (at the time of the snapshot) can claim their TLDs on chain. The icann allocation is 5.8% of the current circulating supply.
i suppose there could have been a way to give ICANN a blank check to modify the handshake namespace in perpetuity, but i suspect that might either be technically unworkable or just made the whole venture pointless.