it's a photometric redshift derived from the lyman break. rest-frame ultra-violet emission less than 912 A is "completely" absorbed by intervening neutral hydrogen, and between 912 and 1216 A partially, in lines. so objects are dark at shorter wavelengths than 1216 A (in the frame of the galaxy). their observations show that in our frame there's no emission short of 1.46 um (infra-red). and 1.46e-6 / 1216e-10 ~ 12 = 1+z, so redshift is approx 11.
if it's correct (photometric redshifts are not as reliable as those obtained from spectra, but are technically easier to achieve, and this is really pushing the limits of what is possible - my partner, who is still in astronomy, is sceptical that this is real), then it's the most distant object known.
i guess the above isn't very clear. i'll try again. hydrogen gas just floating around in space absorbs ultra-violet (UV) light. so you don't see much UV from galaxies.
now distant galaxies are redshifted so much (by expansion of the universe) that the UV ends up in the infra-red (IR). so what you observe are things that are only visible in the IR - everything shorter (optical and UV) in our frame was absorbed (UV) in the galaxy's frame.
so one way to find extremely distance objects is to find things that can only be seen in the IR. what you're actually seeing is the redshifted optical; what you don't see in the optical is what, in the galaxy's frame, is absorbed UV.
but these galaxies are very faint, so they are hard to detect. using a gravitational lens boosts the brightness and so makes this technique more powerful.
i'm not sure that helps (a diagram would make things much clearer). the technique, well, the resulting objects, are called "lyman break galaxies". but i haven't found a good reference googling.