The accusation is that they stole his approach of solving it. If OpenAI didn't bruteforce it with dozens of agents, he would have solved Navier-Stokes eventually since he evidently had the right approach. So knowing which approach to take makes all the difference, if they didn't know the approach they couldn't have solved it.
It's like he had a treasure map and was about to find the treasure, but they copied his treasure map and scooped him with a faster boat and found the treasure first. But he would have found it if it weren't for them.
It's like he had a treasure map and was about to find the treasure, but they copied his treasure map and scooped him with a faster boat and found the treasure first. But he would have found it if it weren't for them.