It’s not soldier proofing although that can be an unintended added benefit. This keeps the bolt from locking prematurely, it’s called an anti-preengagement mechanism.

In the AR-15 and AR-18 the way the bolt head is prevented from locking prematurely is really stupid to be honest, it has the cam pin run along a track in the receiver until it reaches the end of travel. That’s what that little hump on the side of AR-15 uppers is for. This is bad already because it causes an insane amount of friction, but it’s even worse because the AR-15 receiver is made out of aluminum while the cam pin is made of steel so it wears out the receiver even faster. SIG created a “remedy” to this in the MCX by introducing a replaceable track where the friction is the highest and therefore the receiver wear is the worst.

However the solution to this can be done for cheaper and a lot simpler. In the case of the tavor the cam pin is held still by a rod until the bolt head needs to start rotating. In the case of the AK and Garand a shelf was machined into the cam track that kept the bolt from rotating until a starter lug was hit by a cam track in the trunnion that forced the cam lug out of that shelf to allow rotation.

In this case it seems inspired (loosely) by the ARX-160. The ARX-160 had 3 problem’s with anti-preengagement:

1. It was made of plastic nearly completely
2. The bolt head was much more similar to an AK in how it operated than an AR
3. That bolt head was still multilugged like the AR-15.

To solve that Beretta added a pin inside the bolt carrier and a small metal track in the receiver. That metal track holds the pin down, which prevents the bolt from rotating, until it’s time for the bolt to rotate at which point there’s an incline in the metal track that allows the pin to go up which allows the bolt to freely rotate.

Here in the QBZ-191 that pin is replaced by a lever because instead of a normal recoil spring assembly the Chinese went with an AR style buffer tube and AR style bolt and carrier but not T shaped charging handle. Instead of locking the bolt here it locks the cam pin, preventing it from moving which prevents the bolt from moving. Honestly a pretty good design all things considered.