Almost. But with one key difference. PPAs are precompiled binaries where you cannot inspect the source - you have to trust the maintainer of the PPA. AUR is a repository of source packages which you can download and inspect yourself (or hope others have done this). This makes AUR more community focused than PPAs I feel. AUR is also a central repo managed by people that dont own the vast majority of the packages hosted on it and where packages can be taken down if found malicious. PPAs are lots of separate repositories all managed by different people that generally maintain all the packages for their PPA.

Though in both cases anyone can upload anything to them, so they are not 100% trustworthy. But I do think the way AUR works puts them ahead of PPAs.