While IBD is transferred from snake to snake, I don't recall ever reading that IBD could hitchhike on the owner and then be transferred to another collection that way.

I took this from the link posted above:

Exposure to this retrovirus appears to be due to a transfer of body fluids. Breeding, fight wounds, and fecal/oral contamination are common ways of transfer. Casual handling of an infected specimen and then a normal specimen does not appear to create enough viral exposure to cause infection.
Could you post the lab results that your vet gave you? I'm sure we'd all be curious to see exactly what it was.