It is possible & probably that it was patronymic, particularly since Gottlieb was a common first name. But you cannot be absolutely certain. Mainz was on the left bank of the Rhine, which was under French control from the 1790s until 1815. Thus Jews living in Mainz were subject to the 1808 Napoleonic Name Adoption edit which you can find on line (Imperial Decree, Bayonne, 20 July, 1808). Samuel Gottlieb & Sarah are most likely pre-1808 names. I think it they were not, the record would have said Sarah geboren her maiden name. But some Jews, like my ancestors in Speyer, also under French control, had surnames before 1808. My third great grandfather & his son did, but they adopted different first names & surnames in 1808. This may have been done  for patriotic reasons - he named his son Napoleon. But if I had to choose, Moises was born about 1771 & Samuel & Sarah may have died before 1808. You can find the Mainz Name Adoptions on https://www.a-h-b.de/de/projekte/familienforschung/name-adoption-lists  https://www.a-h-b.de/de/projekte/familienforschung/name-adoption-lists/mainz   where you will see that Moises pre 1808 name was Moises Gottlieb & that he likely had a son named Gottlieb Samuel who became Gottlieb Samuel Pfan.
       Jonathan Rose