The glow may very well be deliberate.
As you can see, the circles, the symbols - have the same glow.
It can be as you say for:
1. Deliberate purpose. Why?
a) Tell something to a specific viewer / audience - someone who know the specific meaning of it.
b) Or the random viewer, to Inform us that this may not be precise?
2. Not deliberate
a) It's not a decoding effect from Audacity or imprecise sound. More components would have the glow. We don't see this.
b) Did it happen before embedding due to rescaling / resizing? It's possible, I know a fair bit about that process.
c) Did the original material come from a different source than the rest of the material in the whole recording? Possibly.
3. Why isn't the grid having the glow?
a) Too thin, not heavy enough to make such an imprint?
b) was added later during the embedding process
Regardless - the Circle, symbols - seem to have been created as one entity.
Deliberate or not - we won't know that until we get it into the right context.
IMHO, discussing 'why the glow' without having a proper way to confirm it through testing won't cause anything but more noise while we fight to figure out the more comprehensive pieces.
To be honest - I think the whole delivery through a grainy image also just illustrates that we should try to dive too much into the details - too much grain.
This is deliberate - it's not meant for direct measurements.
However, to illustrate concepts and arithmetics. I'm still convinced that it is perfect to do just this.
If we understand what the concept we should be able to apply the correct parameters - based on a key we're still trying to find.