The populations of both predator and prey species are increasing, I would call that a sign of a healthy population. They are being monitored (as indicated in the article) or the fact of the newly arrived species in the area and the increasing populations would be unknown.
I wouldn't, not yet anyway. That could just mean that the population is reproducing quicker than the radiation can kill them off. What they need to look at is the life expectancy of the given animals verses the same animals living in a non-radiation infected areas. Granted the article states that the animals are healthy but is that compaired to the non-radiation infected animals?
Maybe Jurassic Park had it right:
Dr. Ian Malcolm: No, I'm simply saying that life, uh... finds a way.
From the article it appears that those exposed to weak to moderate radiation may have problems but the survivors give birth to more radiation resistant (or tolerant) offspring which do the same and
evolve the ability to live healthy lives in an environment that killed many of the earlier generations. It will be interesting to see if in another 20 years the mice that have evolved tolerance now for low levels of radiation but can't handle the high level areas have evolved enough tolerance to handle the high level areas too.
I wonder how the mice (or equivalent for the location) are doing in the areas of the orignal bomb tests of 60 years ago? Can they handle more intense radiation than the Chernobyl mice? Is there a maximum tolerance that can be evolved?
Interesting question... Although making the entire planet immune to radiation isn't exactly the way I'd want to make nukes irreverent.