There are a number of real historical references that that make this connection, so it is most likely pretty solid. I have been looking for documented descendants of the Sotelo de Moctezumas as this is one of the alleged ancestries of Petronila de Moctezuma.
There is a brief, tantalizing reference in the Codex Chimalpahin that suggests other Sotelo de Moctezuma descendants, but without naming any of them.
I have only recently seen a document in the Sagrada Mitra de Guadalajara that actually names Petronila de Moctezuma and Martin Navarro. So I am pretty sure they did indeed exist. However, anything of their antecedents, at this point, is pure speculation as there seems to be no information. There is a cryptic reference is some of Jaime Holcomb's work, but I cannot locate it, and no one that I have corresponded with can produce it: so this is of little to no value.
The relevant historical texts do not mention them. They were apparently not involved in the extensive litigation of Moctezuma's descendents to get rights to the various encomiendas handed out by Cortez, or to get grants from the Spanish monarchy. There was too much money involved here not to have been involved, which suggests to me that Petronila de Moctezuma may not have been a descendant of Moctezuma.