It didn't surprise me to find the original was very, very similar to his "work".
Look, if MBTA had commissioned him to create this map (well they'd want their money back) but you could pretty much grease up the lawyers right now, it would be his and their property and Naughty Dog would be implicitly not paying a fee.
However, in this case, his screeches of "my IP" are complete nonsense. In a legal sense he drew a picture of a picture, made several intentional changes and called it an original work, he doesn't hold any IP rights in this case as his picture is of something and for the purpose of something he has no claim to. I believe that he did work hard and probably improved on the design, which is why this must be frustrating for him, but he has to understand his work was a dead end. It was not used to replace the current map, he was never going to make a penny from this. He knew that, yet after putting his redundant map online at a resource that makes it clear the maps are unofficial, he now suddenly believes he deserves money for this.
Someone in the Naughty Dog art department is probably getting told off for this, the only money he could claim is what the game artist would have been paid for his time if he hadn't used Google image search...