@Carl’s statement while correct in that context, can not be used verbatim in other circumstances.
Roon decodes the files, so obviously it knows more than just the “container”. It knows exactly what data it has.
You can easily infer much about the upper bound of what the content can be from the data in its container, but not so with the lower bound.
There is a difference between knowing whether it’s an oil painting or watercolor painting, vs know if it’s a Danny Dulai or Picaso masterpiece.
Notably, it doesn’t even always make sense to know if the file has been upsampled because the artist who created the content may have used 44.1/16 samples for the drums but a microphone with a 96/24 ADC. When the final recording is made at 96/24, is it real or is it upsampled?
So back on the example you commented on, an AAC file that is containing lossy data can not possibly be high quality because the container can not hold lossless data. Whatever comes out of the AAC has to be a degraded form of whatever went in into it.