I doubt the plants are antho free, though as mentioned by others they may look like it. At the very base of the pitchers, where they meet the rhizome, normal plants with little color will show red in the pitcher attachments and the tips of new leaves growing out. Antho-free ones will tend to look almost fluorescent or even nearly translucent at the base.
As for being Okee plants, 20 miles could well be within range for transported seeds, but certainly you'll need to see growth once they're getting full sun, and compare it with normal minors. Even young okee plants will have pitchers half the width relative to height compared to normal plants.
Everything has a reason, whether big or small. Never underestimate the power of what is or is not.
There is far more to everything than meets the eye.
They are certainly too tall to be typical minors but as N a N says could be historic population or transported seed.
If you look down on the rhizome there is normally some red colour at the base of the leaf close to the rhizome visible even in plants that have grown green because of shade, If you cant see any red pigment, remove the adjacent grass and let the sun in you will know in a week or so whether it is anthocyanin free or not.