Github's identification is incorrect, the text is clearly the GPL and not AGPL. My guess is that github does its LICENSE-autodetect thing only on the default branch but displays it everywhere (this probably should be considered a bug?).
I don't understand the hype for v3. There are a number of other secret detection tools out there that leave this in the dust. Plus, for all the money they took on (wasn't it more than $10M?) I'd expect a bigger delta between versions. From the commit history it looks like they superglued this thing together in ~3 months. Looking at the codebase, they also don't seem to know Golang very well.
There are a lot of secret detection tools out there. It probably is going to depend a lot on the specific features you care about. I personally really like shhgit[0] which is MIT licensed and is the tool I've found to most match my workflows.
Gosh, I'm so sorry for spreading false information. Had that license widget not taken up so much screen real estate one might have had a fighting chance at spotting the error :-(
I dread tracking down which issue in the GitHub org that belongs to