I concur. Definitely not any kind of
Lilium. To grow that much without coming above ground leads me to wonder if they did not come from seed at all. Do you remember what the seeds looked like?
Mrs. R.O. Backhouse seeds look like this, no matter who the pollinator was:
The photo was taken with a lighted background. The seeds would have looked darker in color, and you would not be able to see the single line (the embryo) within each seed. Inside the circled area would be nearly opaque, outside would be translucent and paper like.
