LETS LOOK REALISM
400 acre is 1.6 square kilometre =160 ha.
If radius is 1 km, area is 3.14 km2.
Average foraging distance is 2 km
3.14 x 4 = 12 km2 = foraging area. The forest is 10% from that.
50 colonies in the forest. Plus surrounding colonies.
It is clear, that honeydew of oak trees cannot feed hives all the summer. And bees must get pollen from flowers.
It is not take much time to fly outside the forest. It depends how nest hole is situated in the forest. However, location analysis of the secret bee colonies was not correct in the article.
But old oaks offer nest holes, and it is not long distance to foragers fly outside the forest.
So, the oak forest cannot be a reason to offer new unknown ecotype to bees, which devide the genepools from surrounding bees.. The bees basic instinc says, that they must forage in various flower species not only in one type . And they have a short flying trip outside the forest.
If we think 16 hectare rape field, it is not much.
When you put 10 hives on the side of the field, you find the bees forage in the nearest side of the field, but nothing on the opposite side.
Is there any other reason to disconect the small patch from surrounding environment? No, it is not possible.
CONCLUSION: I say that the oak forest is not a reason, that some new subspecies can differientate in that small forest patch. It propably offers much nesting holes to colonies. That is not a reason to differientate from the surrounding genepool of honeybees and from drone mating swarms . Very short distance to bees to fly outside the forest. Under 1 km.
But the story is good.