Depends on what "under the house" means.
If he buried them in the basement (dirt floor, I'd assume), there may not have been much smell.
Also, can any locals chime in? Sometimes during radon remediation, a flue stack is installed running from the basement up through the roof to lower/remove radon from the basement. Is radon found in that area?
Humans are usually not at all good at tracking scents. If the occupants noticed an odour, they may not have realised it was coming from their own house. Or they may have thought they had plumbing problems.
This is all speculation since LE hasn't even confirmed that Sigg said that, let alone released any such information.
Yes, definitely. We have that in our house. (eta: remediation, hopefully no longer we have radon in our house!)