Second hand nexus 5 Q?

I bought this nexus 5 from a previous user, noticed bootloader unlocked, diferente kernel(althought i flashed another already), but something caught my eye, im not sure if i have the stock rom, as i get an update of 16mb and fails.

"devcheck app"
Under system = Codename: Hammerhead
5.1.1
Build: LMY48I

Is this stock?

Facebook (lol) crashing a second loading app on news feed

Does anyone else experience this problem? I am on latest oxygen 2.1, tried with stock kernel and latest ak kernel and have xposed with few modules.

I have had facebook version 46 which had worked perfectly fine until the v47 update from the playstore..which had completely messed the app up. A TBU restore of my previous v46 does the same now...

A clean flash has been done and still problems persist..anyone know of a fix?