This may be easy to explain in case their system doesn’t account for the possibility that whatever DNA they get is not from a dog. Then whatever they answered is just the dog race with DNA closest to human, according to their metrics.

They very likely have a set of possible target DNA references, and look at how close whatever they get is to each of these.

And there are different metrics with which one can measure DNA similarity. Hence it also is to be expected that a different company would return different results. Albeit not super different.