A German scholar near the turn of the last century claimed that this was an "Old German" name from the high Middle Ages, but failed to specify which language, what sources he'd used, or what date that he was tracing this etymology back to. The transliteration is of "griep" = grab(ber) "en"= in "trog" = trough/vat/till.
The late-19th Century's scholar's suggested that this was a "dough kneader" and/or a journeyman baker. It had not made sense to me why a guild-based economy would stop or would "freeze" a person's name or title so early into their career track as journeyman. Why not "Becker" or "Bäker" or some derivation instead?
I have read enough on the area: Baltic feudal low-German-speaking duchies, to get to a theory about it: prejudice & guild discrimination against the indigenous West Slavic / Wendish people, not allowing Wends to be guild members, thus stopping the title at an apprentice. This is incomplete, however.
Alt Friesin / Old Frisian and Slavonic languages hold more possibilities related more to place names than to an occupation: "iepen" = open in Old Frisian, and "trog" can translate to a trench, perhaps a canal/ dyke. There is a large family study by a Dutch woman of the name "Griep" , that covers more than six ethnicities, for places that were Hansa / Hanseatic League free cities. This would also make a plausible etymology of specifying, "the Griep (merchant or trading family) located in the quay or the canal lagoon" that would match Stettin Pomerania. My Griepentrog ancestor emigrated from Stettin/ Szezscin in 1881, and I have several DNA matches w/ Dutch/ Zeeland FTDNA members & South Africans while few matches among Germans or Danes.
I would more suspect that this 1890s linguist was oversimplifying & was influenced by German nationalism & largely speculated his way to "grabber in the vat" until things sounded plausible.