Glencoe-like fruit from Black raspberry seed!

During early 2019, I sowed seed of black raspberry, Rubus occidentalis Ex-Black Hawk. The seed were harvested from some plants in my garden received originally as seed from Seed Savers Exchange in 2003. They germinated around 26th May 2021 and I planted about 20 quite close together with the thought of later moving them to a permanent place. That never happened and the plants grew large and started producing last year.
To my surprise I discovered that some of the berries, presumably from one of the plants, were very different and reminiscent of the hybrid with red raspberry (Rubus idaeus) “Glencoe”.
About ‘Glen Coe’: “this is the result of a cross-breeding between Rubus idaeus ‘Glen Prosen’ – a local Scottish variety with red fruits – and R. occidentalis ‘Munger’, a black-fruited variety from North America that was introduced in 1897 and extensively cultivated on more than 600 hectares in Oregon. This hybrid was developed by the Scottish Crops Research Institute, an agricultural research centre near Dundee (now integrated into the James Hutton Institute). Introduced to the market in 1989, ‘Glen Coe’ still surprises with the unique colour of its fruits, which is intermediate between its two parents.”