If I didn't know any better I'd say it was a marketing ploy.
Hell, the first time I saw the layout in use was on knowyourmeme.
What's next? Patents on rounded corners?
I understand saying something like this when it may be a complete rip-off, but people get up in arms these days even if something is 5% similar to something else. That really bothers me, as that world actually works like that. Everyone creates "new" stuff based or other people's work or inspired by them, so of course they will be at least somewhat similar. But they are acting as if the world doesn't work like that.
As for Pinterest, I guess they dominate references to the dynamic grid layout as they popularised it with the masses, so it's an identifiable reference for those who otherwise might not know what's meant by 'dynamic grid'.