Totally a real thing. Apparently it is a type of preserve called Varenye. The pine cone version comes specifically from regions in Siberia which actually makes a lot of sense. About the only plant that has historically grown in abundance across the Siberian taiga are conifer trees. It is no wonder that humans figured out some way to eat them (you can also make tea from the needles). Here is a recipe I found that modifies it a bit from the original to make it more palatable.

Don’t you wish all this was in the LN you read? The world of jam making is richer and fuller than I had thought!