That's interesting. Unfortunately, AVG has been acquired by Avast last year [1]. I already looked into the new version of AVG a few months ago, and found that they have replaced AVG's engine with Avast's engine. Since the scanner always runs as NTAuthority\SYSTEM in the current Avast version, I would assume that the same is true for the most recent AVG version. I'm not completely sure, though, so don't quote me on that.

[1]: https://press.avast.com/avast-announces-agreement-to-acquire...