"...dated 1932..."

They're not just claiming Kane/Finger ripped off this idea... they're saying this predates Siegel & Schuster!

Good luck with that.

It looks legit, to be honest.
As an artist myself, I can see the seeds being there, which later evolved into Batman.
But if anything is right out stolen, it's mostly only the name.
And I doubt Finger knew anything about any of this..

First, there's no copyright issue with the name "Batman". It's a trademark, and one that this Foster guy never established. Second, this "Superhero"  looks nothing like Kane's early designs OR the character that Finger helped develop. And that's just visually- The complexities of the early character's backstory are not in evidence.

Second, although there is no evidence of great artistic talent in the work of this Foster guy, he seemed to be a notch or two above Bob Kane. Why would an editor or somebody on staff at the comics company hand samples of a concept off to a freelance artist (one who wasn't all that great) so that he could present it as "his own work"? Foster claims he left samples witth the editorial office. If the company had ripped him off, they would have claimed ownership of the character directly and pulled Kane and Finger in as strictly work for hire. Or more likely, hired Foster.

This is just a silly coincidence that some guy and his family have been stewing over for 70 years. Just looking at the mountains of  material about the early stages of Batman's development is enough to dismiss this as silly.

To top it all off, the differences between Foster's concept and Kane/Finger's concept is so great that even if Kane had stolen the name from Foster, there would not be enough grounds to sue.  Not even back then , when DC managed to sue Fawcett over Captain Marvel despite the substantial differences.