In the video below it’s clear that Hamilton is behind the safety car when he crosses the second safety car line, then overtakes the safety car. That explains why he got a penalty under article 40.7 of the sporting regulations which says:

With the following exceptions, no car may overtake until it has passed the first safety car line for the first time when the safety car is returning to the pits. [...] Any car leaving the pits may be overtaken by another car on the track before it crosses the second safety car line.

However it looks as though Hamilton could have reached the second safety car line before the safety car, but slowed down before he got there. Why was that?

Perhaps he was fully aware of his obligations under the rules and chose to slow down to hold up the Ferraris, hoping he could get ahead of the safety car but they could not.