In several forums there are comments about surnames being Jewish just because the Inquisition condenmed a person carrying that surname of practicing Judaism. A person does not make all individuals carrying that surname Jewish.
Sometimes is just the etymology of the surname that points in that direction. But the etymology of a word does not mean that a surname is Jewish.
A good example is Mejia, my surname. It could come from Mesias that is a Jewish name, but because Spain is Catholic, we use many word from the Bible including Messiah. Do I carry Mejia because a Catholic took Mexias as surname (the kind of invented or ornamental surnames), or because I had an ancestor that was a Jew?
It is the same with my first name Jose. Of course Jose is a Jewish name, but I carry it because my mother wanted to honor San Jose, not because I am Jew.
Mejia could also come from Megia an ancient word in Spanish meaning "medicine" or drug. Was the first Mejia a "pharmacist" a "boticario" as we call it? The surname could be a trade name. Or it could be a corruption of "Matías" a first name, which would make Mejia a patronimic as the "Diccionario de Apellidos Españoles" by Roberto Faure, Maria Asuncion Ribes and Antonio Garcia (Madrid: Espasa Calpe, 2001) explains.
Moreover, do I descend from a Sephardic Jew that came to the Americas with Mejia or Mexia as surname, or from an Indian who was forced to baptize and given a Spanish surname by the priest? Or maybe from a slave that also was forced to baptize and take a Spanish surname, a "Christian" name.
In colonial times in my country, Nicaragua, there was a “de la Cerda” owner of three slaves that carried the “de la Cerda” surnames just because there were part of the “family” meaning the people part of the house, but not related by blood.
Many family accepted children to be reared as “hijos de casa” (children of the house) who were working as maids or helpers without being paid for the work. The “parents” provided them with food, cloths, medicines, gave them basic education, etc. Many of them adopted the family surname and were known later in life by that surname, even though they were not blood related.
The same applies to many other etymologies like Dagoberto, Alberto, Roberto, etc. all names with German etymology. But that is not enough to say that you have a German ancestor.
My son-in-law is a white American with a German surname. He told me that really his family does not have German ancestors. They took the surname after a German family that protected Indian mix blood from deportation from Florida to Oklahoma. His ancestors were able to pass as whites under a German surname.
The litmus test of the Jewish origin of any surname should be the family tradition or the cultural practices of the family like foods or ceremonies including burial practices.