Boundaries like that are not unusual. Our property, is a lopsided "U", with the large leg being ~400' and the narrow leg about 60'. The original land, which dates back to the mid 1700's included farm land on both sides of the road, as does the farm down the street from us. At some point the land on the opposite side of the road was sold, but when we bought the place ~19 years ago the dug well was still on the other side of the road, for which we have an easement (it's been replaced with a drilled well on our property).
After the land across the road was sold, what eventually because our property was a roughly 12 acre square. The previous owner then old a 2 acre chunk to his son for their house off to one side, but not completely on the corner, so our property completely surrounds the son's 2 acre lot. Apparently the original narrow leg was about 100' wide but he also traded a 40' wide slice from that side to the far neighbor in exchange for ~3 acres of unbuildable land along the back of the property so the neighbor would have sufficient frontage to build their house. I have no idea why he didn't use either opportunity to square out that corner, but as a result we now have a ~60' x ~200' slice of our property that is essentially unusable.
So a 6 acre tab extending into another piece of property is completely believable.