Merc had a radio call early on to HAM saying to do the opposite of RAI.
Ferrari came out first, so Merc followed just incase Ferrari did a dummy (which if you watch the pitlane feed, they did IIRC 2-3 times).
All teams to dummys. Its not new. It's done just incase the other team do something unexpected. Dont be acting like its just Merc doing it because its not. I do not support or condone it, but it had bugger all to do with todays result, nor had any impact on anything in the race.