As others have said in the comments it’s impossible to know for sure without knowing the inner workings of Black Library. However my inclination is to say no and attempt to explain why I say that in my answer. Obviously I’ll put in the disclaimer that I don’t work for Games Workshop and therefore my answer is purely based on my understanding of the fluff.
When mortals undergo the process to transform them into the Adeptus Astartes aside from the more obvious aspects (growing two feet in height, gaining strength, speed, and intelligence) they also take on aspects of their gene-sires. This is because their Primarchs are the source of the genetic material for their legions (and successor chapters).
This goes beyond fighting style. Blood Angels are often described as especially beautiful, Space Wolves are great hairy guys, and Salamanders are all dark skinned with red eyes (bear in mind that originally not all legionaries were from the Primarchs’ planets, many came from Terra so these must be gene-seed/genetic rather than environmental/cultural.
The Luna Wolves and Alpha Legion experienced this to the extreme. Alpha Legionaries all look pretty much identical and almost the same as their Primarchs. The Luna Wolves had a number of individuals, known as the True Sons of Horus who didn't just look a bit like their Primarch but appear as diminutive duplicates. Horus Aximand (Little Horus) was one, Ezekyle Abbadon was another. It’s safe to assume that this was as a result of the gene-seed implantation rather than two mortals from Cthona looking identical to a Primarch who was created on Terra before being lost to the warp. It's not entirely sure whether Little Horus was Terran born or from Cthona but Ezekyle Abbadon was the son of a Cthonan warlord.
In short, Abbadon is not a clone of Horus, a primarch’s biology is utterly beyond that of even an Astartes. He’s a True Son of Horus, one of the few in his gene-lineage who’s appearance changed to be almost exactly like him.