That was indeed 2.8 at racing speed, as they maintained that speed (save for keeping left to avoid the debris field and then Russell) up until the safety car notification came out. I believe that both were actually clear of the debris field before the local yellow for that, which was only there momentarily before the safety car. It was at the exit of the hairpin that that the SC was called, Oscar accelerated down the straight, and Lando pretty much didn't.

The actual amount that you are allowed to slow down is kind of nebulous. When the safety car comes out, per sporting code 55.7 there is a delta time that the drivers must stay above (which is to say, be slower than). The stewards' decision makes no mention of this code section or the associated penalties described therein, so Lando was presumably within this parameter, which is to say that he was driving slowly as directed by the sporting code. This is the parameter that he mentioned in the interview.

This means that the crux of the issue is sporting code 55.5, which, among other things, directs that under safety car conditions that no car may be driven UNNECESSARILY slowly. See what I mean about nebulous? There is the hard delta, but then gray area between that and barely creeping along. It comes down to conditions on the track and the stewards' judgment. In this case, the track conditions relating to his competitors were the problem. As Lando was going along slowly, Charles was tucked in behind him. Neither him nor Ferrari were cross on the radio about pace. Alex, however, was tucked in behind Charles and noted on the straight that "the Mclaren is holding back". Further drivers accumulated in the train heading down casino.

Sporting code 55.5 doesn't have any specific codified penalties enumerated therein, but impeding other drivers by building a gap ahead when they are unable to pass due to the safety car condition (save for positions gained on the pit cycle) is unacceptable. That's why they had to go with a breach of sporting ethics instead. As an aside, the track map graphic was up when all of this was going on (at least on F1TV), and the vast gulf that developed after Oscar followed by the Lando train had me with my head in my hands.