Turns out the hand writing matched the owner's hand writing letter for letter.

That's literally how everyone writes those letters. Hell, that's how
I write.
Not only that, but how can that be true when this was spray-painted on a wall? People's penmanship doesn't translate into spray-can writing. The reflexes are all different and you can even see how the stroke pattern on the 'G' is different because two separate strokes were necessary.
Also, graphology is largely bullstuff pseudoscience and there's no body of evidence suggesting that experts can 'match' someone's writing to a text with reasonable certainty.
https://www.nashvilletnlaw.com/blog/handwriting_brown townysis_and_the_l/