Makes sense but it's still surprising that the back truck chassis went under the front truck. I guess whatever crash protection the back of the front truck had either failed or was missing.

It's common for trucks to slipstream each other to save fuel, but sadly this is what happens if the front truck has to suddenly brake.

As truckers (sometimes) do it was trailing another truck with trailer. Then the front one did a braky and the rear one did not.

It looks like the trailer was empty. But what I could find is that they transport food stuff (bread and pastries).

Holy Fuck! What the hell did it hit? I've seen truck cabs come off the chassis before in accidents but never one perfectly pushed back in to the cargo area.
Looking at the cab there is a fair chance the driver is ok, probably battered and bruised, but ok.