I think for a while leading up to the recent session stealing hack, there has been a massive amount of positivity from Lemmy users around all kinds of new Lemmy apps, frontends, and tools that have been popping up lately.
Positivity is great, but please be aware that basically all of these things work by asking for complete access to your account. When you enter your Lemmy password into any third party tool, they are not just getting access to your session (which is what was stolen from some users during the recent hack), they also get the ability to generate more sessions in the future without your knowledge. This means that even if an admin resets all sessions and kicks all users out, anybody with your password can of course still take over your account!
This isn’t to say that any current Lemmy app developers are for sure out to get you, but at this point, it’s quite clear that there are malicious folks out there. Creating a Lemmy app seems like a completely easy vector to attack users right now, considering how trusting everybody has been. So please be careful about what code you run on your devices, and who you trust with your credentials!
I think their point is password managers make it very easy to have completely unique passwords, and if your Lemmy password is compromised you can change it without worrying about any other accounts being compromised. Not that a manager would magically protect you from ever being compromised.