I too wondered why they felt the need to apoligise for that, it’s not like the tweet told us anything we did not already know. I’m sure Mr. Putin could equally truthfully put his name to a similar tweet. The difference perhaps is Putin is sufficiently aware to understand he does not need to.
All that has changed is we now have it officially conformed that some sections of the US military high command are trigger happy meatheads. But that isn’t going to surprose many people either.