I'm a breeder from belgium who really likes old heritage breeds. In our country we have a breed that is named "Doornikse kriel" (kriel is dutch for bantam) and it really struck me to see the pictures of this swedish breed as they are almost totally similar. I guessed they share the same genetic background seen the fact belgium is so close to the nordic countries and was raided by the vikings.
You are probably correct. Another characteristic I've noticed is that landrace birds all share the speckled white feathers - similar to the Swedish Flower Hens, Hedemoras, and others that escape my memory.
But yes, I notice the same similarities in breeds - especially between the Braekel, Fayoumi, Campine, Friesian, Westphalian, and/or Gull-type breeds of which there are numerous.