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.
