The problem with the Android version is you got three apps in your app drawer when installing the main Facebook app. That was confusing, spammy, and impossible for the user to opt out of if they wanted to use Facebook on Android at all. A separate app is just confusing (unless you are coming from Facebook's perspective), so it is an improvement. I am positive there will be a separate Android app in the coming weeks.
The Android shortcut was really confusing - a guy at our local watering hole last week was showing me his favorite Android apps, then pointed out an app he installed because his camera app broke. "It just stopped working last week, but I installed this app and use it instead, it works. Don't know what happened to my camera."
Turns out that the Facebook Camera shortcut just said "Camera" - and of course it didn't open up the stock camera app (I think it showed up on the main screen and first in the apps list, too). Once he updated Facebook and the shortcut disappeared, the stock camera app was more obvious.
The shortcut itself was really confusing - it said Camera on it and it wasn't immediately obvious that it was Facebook-specific. You want to take a picture, you look down & see "Camera," and you click on it. Combine that with the fact that icons change underneath you a lot anyway (see also "Android Market becomes Google Play Store"), and you just default to reading the app name anyway; so you tap to open the first app whose caption matches what you're looking for.
I mean, why would anything but your stock camera app be named "Camera," anyway?
Yeah, the "Camera" thing was confusing. They later added a little white F in a blue circle to the bottom-right of the icon. But before that, I thought it was something my launcher had added, since there were two Camera and two Messenger apps.
"A separate app is just confusing" Is this not a new separate app on iOS? I realise it's not installed alongside the Facebook and Messenger app as it was on Android but it's still separate of the main application.