Two-pane email browsing was been around for more than a decade. It was used by Outlook and in other email clients as well.
No. It was invented by Steve Jobs shortly after he designed the wheel.
I'm just pointing out that they seem to have copied UISplitView exactly, including how it adopts to smaller screens and landscape vs. portrait orientation. Split screens have been around for a while, but this implementation is very specific.
If you don't want your ideas to be "stolen", keep them to yourself.
You put the word "stolen" in quotes. Whom are you quoting? The post to which you replied did not say that Google had stolen the ideas, it said that Google had copied the ideas.