They were angry when Rosberg made contact with Hamilton and made them lose the race. It's clear that in the previous race Rosberg staged two errors to let Hamilton by, hoping this would be enough to be square and make peace with the team. But it wasn't enough and Mercedes have decided Hamilton will win the championship, they will stage more failures if necessary. This is probably right because Rosberg is dishonest and would crash into Hamilton again to win. Rosberg has zero chance of winning the championship because Mercedes would stop his car, so the only rival is Ricciardo.