Yeah, I'm unsure why they wrote that. In their 8.3 pet guide they didn't mention them at all. I guess I could ask Perculia, but a couple of theories:
(i) it was possibly just a mistake
or
(ii) there's a good chance (though not 100%) that the *rocket* chicken in Mechagon will be tameable. The daily just hasn't been up yet for us to check. If that's the case then it may have shown up in Wowhead datamining and hence they wrote "mechanical chicken" in that headline.