I think he means the Mercedes cooling error, which made them lift and coast for 300-400 m before the corner.
Basically Merc were just sailing along this Weekend; indeed RBR was faster all things considering (not their fault the competitors calculated wrongly). But Merc don’t usually persist in their errors so it’s hard to think RBR will be able to replicate that soon.
According to a Merc engineer:
In the latest episode of its Pure Pitwall, trackside engineering director Andrew Shovlin reveals the cause of Mercedes Spielberg issue.
"Fundamentally the car doesn't have big enough radiators," he says, "and that's something that we were a bit optimistic with, how much we could get out of the cooling system.
"It's underdelivered to what we hoped we could achieve," he admits, "and it's meant that we are carrying this issue where in the very hot races we will be struggling to keep everything cool enough.
"You can increase the amount of cooling you get out of the car by opening up the bodywork exits and in Austria it was 35 degrees, that actually put us at the upper end of what we could achieve just by opening the car up. So, we were on limit. When you get to that point you are really limited in your options. You can start to use lift and coast, which is where the drivers get towards the end of the straight and they back off the throttle. They then brake a bit later and you have a period where the car is just coasting into the corner, the engine is not doing work and you can lose a fair bit of temperature like that.
"But, as you saw in the race, we were having to ask our drivers to increase that to around 400 metres per lap and that is why they were so compromised on performance.
"You can also turn the engine down a bit, then it will generate less heat, but you've got less power and you are slower on the straights."
"It was definitely a significant limitation in Austria," he admits. "We are working on systems, we were working on them before Austria, to try and improve this problem and we should be in a better position. But, it all really goes down to the fundamental design of the car, where in the push for very, very tight packaging, we have ended up being undercooled overall."
Mercedes have built an absolute monster of a car, but by their own admission they have sacrificed cooling for aerodynamics/packaging (as they all do to some extent) which cost them here with the high ambient temperatures. I guess you could call this an error, but if they had not made this "error" their car wouldn't have been so strong elsewhere, so that's in my opinion not a correct way of looking at it. It's not like they've made a mistake on the day, or went the wrong way with their development. They just took a design risk and on this one occasion it's come back to bite them a bit, which they may feel is more than compensated by being faster in less hot conditions. If we go down the path of calling this an error every design decision that comes with compromise can be considered an error in certain specific conditions even if it brings more performance over the season.
Anyway, Mercedes will probably be working hard to develop a car with bigger air intakes, but that in itself will also compromise their performance on the days where they need to deploy it, so it's too simplistic to look at this as any old mistake that they are unlikely to make again and to assume they will be back to being dominant whatever the circumstances on the day. Their car has strengths and weaknesses, just like every other car and it can be beaten (should have been beaten a few times more already this season).