I'm a little bit confused.
My ATV3 got it's update too, but it was not 8.4.2 as mentioned in the article, but 7.2.2.
According to ipsw.me , it should be 8.4.2 for both, the 2013 model and for the original ATV3, i have.
I didn't see it last night when i updated my apple tv.... I wonder whats taking so long