The connections in such big events are the best one can pay. But for latency internet speed doesn't matter, but the distance between you and the datacenter + the route the data takes on its trajectory.
And they are claiming the closest data center which was serving the stream at E3 was 400 miles away. If true, then game streaming tech has gotten a huge leap.
Not sure what to believe. Afaik it was supposed to run on actual xbox one hardware at the data center, 4 XBox One S consoles per server blade.
That 400 mile distance in a straight line through fibre cable in a single hop would take light 6.2 ms round trip. Add video encoding at the server side, video decoding at the other side. Only 4ms slower than running on a local XBox One S is simply not possible.
And indeed, real world will be different with data throttling, jitter, many hops to get to the server, home connection likely shared with other people streaming stuff. Remote play in home adds 60ms on top of the game...