Lyles looks extremely fluid in the last 50m. He should run a very fast 400m as well (he also ran the terrific indoor 300m this year). He is legit and should be a medal contender for many years. This is tied for the world lead but is superior to Van Niekerk's run given the altitude advantage WVN had. It is tied also for 151st all time and one of only five guys to break 20 under the age of 20.
He showed right out of the gate that he was prepared and unafraid of this kind of competition on the Diamond League halfway around the world. A one-tenth of a second improvement would put him to 67th all-time; a two-tenth of a second improvement would put him to 31st; and with a 19.60, he'd move to 17th all-time. So, he really is not very far away at all from joining the all-time greats and it is entirely reasonable to think that a 19 year old sprinter just entering the pros, and dropping almost two-tenths of a second his first time as a pro outdoors, is going to continue to drop time and get faster for a few years.
With him, Kerley, Merritt, and probably Tony McQuay, the 4x400m could go 2:56 this year, possibly 2:55.