You're absolutely right, it is odd that someone is operating the twitter account. Is this Assange's cat or the embassy's?

I don't think we can read in to how Assange isn't in the photo or that the cat is younger in the photo. We know the cat is still there, and even if Wikileaks was still independent somehow and we're just overreacting, that is a pretty great picture which goes with the tweet quite nicely.