I'm not sure how the passage you quoted is in disagreement with your comment.
Sure, WP7 was the first major phone operating system to go flat. However, that doesn't have anything to do with the fact that a major design difference between iOS and Android in the last year or two has been that Android is 'flat' and iOS is not.
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Skeuomorphism used to be a huge red line that divided iOS and Android design
Not true. The original Android design was not flat. It's WP7 that introduced flat design; and Android basically copied it.
I'm not sure how the passage you quoted is in disagreement with your comment.
Sure, WP7 was the first major phone operating system to go flat. However, that doesn't have anything to do with the fact that a major design difference between iOS and Android in the last year or two has been that Android is 'flat' and iOS is not.