Rereading that, it sounds to me as if the opossums eat ticks that get on the 'possum.
However, the numbers cited (5k in a year) are not totally insane.
Assumptions:
200 day tick season.
Opossum picks up 25 ticks a day, in a badly tick infested acre. (Heck, I had an episode as a kid where I ran through a field on an often used path (by us kids) and picked up over 100 ticks in under 5 minutes. It was almost like a nightmare with this army of ticks crawling up my legs & me pulling them off just fast enough to keep them from reaching the bottom edge of my shorts!)
200 x 25 = 5000 ticks.
Yeeesshh!
Opossums don’t go scavenging for ticks, they groom those that are on them.
I’ve seen articles like this posted on neighborhood boards where envirowackjobs are trying to argue for no human intervention in wildlife (despite leaving out food for feral cats, which only attracts vermin, possums included).
For whatever reason, they love opossums. I don’t, and when they get in my yard, my dogs and I make sure they don’t come back.