But "eLife was founded in 2011 by the Howard Hughes Medical Institute, the Max Planck Society and the Wellcome Trust ", so they seem legit.
But nitric oxide (NO) can spontaneously react to nitrite (NO2-) and nitrate (NO3-), and nitrate can actually be used as an electron acceptor by some bacteria in mouse intestines. (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3705454/)
The article points out that wasps transfer protective bacteria to their larvae, so it could have been that secreting NO is really just an indirect way of cultivating more of these helpful bacteria. However, they showed that the protective effect against mold was the same whether or not nitrate was present, which shows that the mechanism really is direct killing of the mold by the eggs themselves!