Roadhog's hook is like one of those old maths problems with the trains. If Hook X is approaching Sombra Y at a speed anchored to this reality only by wishful thinking, and Sombra Y decides to briefly exit this reality altogether by teleporting, who wins?
Roadhog's hook is busted. Blizzard fully acknowledges this, and they're currently working on what they're calling "Hook 2.0". For now, though, it's in, uh, quite a state. Observe, in this video by the esteemed meme lord:
To recap: The hook appears to land after Sombra warps, but it still latches on and proceeds to yank her from the place she teleported to. Across pretty much the entire map. Through buildings.
So, what happened? Players are still trying to figure out exactly how Sombra's teleport works, but leading theories suggest that either her model moves before her hitbox does, creating a split-second window where you can still be affected by attacks after you've poofed away to your safety corner, or her teleport is more of a high-speed dash that can be interrupted. There's also latency to consider. Generally, Overwatch is supposed to favour the shooter over the shootee.
Regardless, this kind of thing, while hilarious, reeeeeeeally shouldn't be happening. Hook 2.0 can't come soon enough.