How did Apple create this animation?

How did they build the animated reflection on the phones on https://www.apple.com/iphone-7/ ? There doesn't seem to be any video element there, only a canvas. When inspecting the network panel I noticed these weird images: https://images.apple.com/media/us/iphone-7/2016/5937a0dc_edb0_4343_af1c_41ff71808fe5/overview/hero-b/flow/large/flow/flow_001.jpg

Is this some kind of JS animation library? Super weird!