From the onboard:
There was no flag signal on the panels when he overtook the McL.
It starts flashing (edit: it's red) when he came up to the Haas, the Haas at that point was way slower than him and he overtook it going really slowly.
The second panel was off without anything on it.
The physical flag gets popped out after they are all past that post.
The precedent mentioned on sky
Decision - Car 33 - alleged overtaking under red flags
edit: here's the onboard
https://streamja.com/92RLv
No clue how synced the team radio is in the F1TV onboard channel but the message comes in the corner