Bellulornis is just mentioned in a single sentence in this work:
Several newly reported ornithuromorphs from the Jiufotang Formation, including Archaeorhynchus, Schizooura, and Bellulornis, have begun to close the morphological gap between Enantiornithes and Ornithuromorpha [44–46], suggesting rapid rates of speciation and morphological diversification during the course of their early history.
It is neither "accompanied by a description or definition that states in words characters that are purported to differentiate the taxon", nor "accompanied by a bibliographic reference to such a published statement", nor "proposed expressly as a new replacement name (nomen novum) for" Bellulia Wang et al. 2016 (which is not even cited at all).
It is also not "explicitly indicated as intentionally new".
If this name has not been introduced validly elsewhere yet, it is a nomen nudum here, as it fails to comply to Articles 13.1 and 16.1 of the ICZN.