Hec's charge auto-knockback is really broken (from a clarity standpoint). I stunned one as Bard as he was running toward me and he still auto'd me while stunned. I've seen other champs CC him and still get hit as well.
From what I can guess, Hec has a mini-dash at the start of the empowered auto, and so he starts his auto from a significantly further away position than players expect (and his attack animation doesn't start until after the mini-dash animation ends). Once the auto has been initiated, it completes, regardless of any other cc effects or range issues (this is true for any champ, and why you can't flash away from autos). In this case, due to the mini-dash and attack frame/animation delay, it is very irritating to see a Hec attack while CC'd or out of range, even though game rules show this to be acceptable due to the auto-attack nature of the empowered hit.