Although "invisible" could refer a provisional c/o, I think that in this case, they're probably asking for tubular (aka kitchener c/o). I say this because a provisional c/o would not really be interchangeable with half hitch. Caveat: if you're not starting out with single rib, then it's probably not tubular. If you are, then I'm almost positive that you want tubular.
Half hitch can refer to either backward loop (aka single) or long tail (aka double) c/o depending on the source.
There is no right way to knit; there is no wrong way to knit. So if anybody kindly tells you that what you are doing is "wrong," don't take umbrage; they mean well. Smile submissively, and listen, keeping your disagreement on an entirely mental level. They may be right, in this particular case, and even if not, they may drop off pieces of information which will come in very handy if you file them away carefully in your brain for future reference.