They would like to have you believe otherwise through their PR efforts, but I wouldn't trust them simply on the fact that they claim they are open source when they are not, and it's not clear what's going on in that binary lib. If they never claimed to be open source in the first place, it would be a different story.
Ehm, the "jni/" directory contains the source for those files. Running "ndk-build" (from Android NDK) in top-level dir will recompile them.
Looking at the source the libraries contain AES code, libjpeg, libwebp and libyuv to handle image decoding, some image blur algorithms and video NV21-YUV conversion routines.
Nothing out of the ordinary for an Android app - offloading CPU intensive stuff to C/C++ where it's almost always noticably slower.
Can you please, PLEASE, check your facts before jumping the gun next time?
Q: Why not open source everything?
All code will be released eventually. We started with the
most useful parts — a well-documented API that allows developers to build new Telegram apps, and open source clients that can be verified by security specialists.
There is Telegram-FOSS [0]. I believe they have removed the binaries. It's also the version you can find on F-Droid.
Edit: Also, the maintainer of the Android app is making all his changes locally and then submits all of them in one giant commit. There are pull requests, but he just includes these in his giant commits.
People do have complained about this [1][2], but he obviously doesn't (want to) understand git.
Looking at it, the libs/arch/.so files are just compiled JNI/NDK libraries compiled from source of jni/* files (that's completely standard for native code on Android). Usually the compiled libs aren't checked into the source control though.
Taking my paranoid glasses off, I'd guess they're checked in so contributors don't have to deal with setting up NDK to compile the app.
https://github.com/DrKLO/Telegram/tree/master/TMessagesProj/...
They would like to have you believe otherwise through their PR efforts, but I wouldn't trust them simply on the fact that they claim they are open source when they are not, and it's not clear what's going on in that binary lib. If they never claimed to be open source in the first place, it would be a different story.