Manor is consistent with the stories availabe at the time. For
one thing, Eastern European vampire stories had circulated for years, and
some of the first written translations from the Eastern European languages
were into German, and were circulating in the mid-to-late 18th century (1700s).
Who knows about the word of mouth circulation of stories, which would have started much earlier.
Ulrichs is dealing with a revenant tale, which is what the vampire essentially is.
A revenant is someone who comes back from the dead (from the French revenir, or perhaps even earlier, which means "to come back"). Revenants don't always drink blood, but unlike ghosts, they do have a physical form. They're stuck between two worlds, essentially, not really living but not really dead. Hence, the "undead."
What Ulrichs did is place the mythology squarely in Nordic tradition, borrowing somewhat from the Eastern European tradition (everyone did this, by the way -- borrow from the Eastern European tradition). That's also
what Bram Stoker did, except he placed the Eastern European revenant not only in
the English tradition but also in an urban area and (for the time) in the modern day. What Ulrichs did is keep the traditional rural feel of the folklore.
The story -- like all vampire stories, really -- has a link to ancient folktales (Greek and Roman ones have been recorded, and the tales
themselves are much older) about mysterious strangers who come and go (and who often
turn out to be demons of some kind or the wandering undead), seducing loved ones and causing -- or threatening to cause -- their deaths. Victims of suicide, tragic deaths and/or accidents are usually the ones who come back in such a state. Manor's drowning at sea is a case in point.
The only thing in Ulrichs' story that I haven't seen before -- although it makes sense -- is this: the tapered stake being necessary to hold the body secure in the grave.
"Homosexuality and Vampirism"
To Manor by Karl Heinrich Ulrichs