  The enhancement of carbon-14 in tree rings around AD 774/775 has generated
wide interest in solar activity at that time. The historical auroral records
have been examined critically. Of particular interest was the "white vapour"
observed in China on AD 776 January 12/13. Both Usoskin et al. (2013, Astron.
Astrophys. 55, L3; U13) and Stephenson (2015, Adv. Sp. Res. 55, 1537; S15)
interpreted this record as an auroral display. Subsequently, Neuh\"auser and
Neuh\"auser (2015, Astron. Nachr. 336, 225; NN15) proposed five "criteria" for
the likeliness of aurorae and on this basis rejected an auroral interpretation.
Instead, they interpreted it as a lunar halo, and suggested there were no
auroral records as a proxy of solar activity in the interval AD 774-785. We
consider if their "lunar halo hypothesis" and their auroral criteria could be
of use in future researches on historical auroral candidates. We first show a
counter-example for the lunar halo hypothesis from a parallel record on 1882
November 17, which was seen as a whitish colour, in the southerly direction,
and near the Moon. We then consider NN15's criteria on colour, direction, and
sky brightness and investigate other counter-examples from early-modern auroral
observations. We also consider the extension of the white vapour in AD 776
according to the distribution of Chinese asterisms, and show that its large
extension was inconsistent with the lunar halo hypothesis. Conversely, the
streaks of white vapour penetrating the eight Chinese asterisms can be
reproduced if we consider auroral-ray structures at altitudes between 97 km and
170 km, along geomagnetic field lines between the L-shells L=1.55 and 1.64. Our
investigations show that we should consider candidate auroral records in
historical documents not on the basis of the newly suggested a priori criteria
by NN15 but on all the available observational evidence.
