We can only guess at this point. My guess is their quarantine area was not large enough and the area outside it became contaminated. They were disposing buckets of waste. Where was it going? Was it protected from animals, etc. who could have moved the virus outside the quarantine area? It lives 6 days outside a host.
On the ground, on a boot, on a hand, in an eye. That’s my guess.
Would our water treatment facilities and septic systems kill the infected waste/virus? Just curious.
Your idea that the quarantine area isn’t large enough seems right. However, it seems to me that the idea that it can only be transmitted from contact with bodily fluids is blown away. Six days outside the host on a surface such as the ground sounds very long for a virus, doesn’t it?