That link shows a very peculiar case. Firstly the POS engine has a head design which only has 3 cam bearings - I call this cheap $#%@@! design - specially for a diesel.
The camshaft broke from stress. the one cam drives the other via meshed gear. Cant comment on what went on with that engine.
Such fracture is also seen in toyota 2C when the timing belt breaks - the camshaft is very brittle - a little example is that it will shatter like glass if you drop it on the floor. That is why a foam and plastic lined container is kept nearby to store the camshaft.
Now back to the bearing bit, yes the camshaft has bearings but they are simply machined into the head - some engines have these as replaceable shells like the crank, but most have it as a simple casting with a precision finish and an oiling hole. The camshafts are usually hollow to aid cooling via oil.
The camshaft is tightened in a proper technique and very evenly to make sure it does not crack. If you recall you once posted a BMW engine - the camshaft was loosened in a very special sequence otherwise it will fracture due to stress from the springs - hence it was rotated so that it could be controlled. In that same BMW engine or even your average DOHC 4 valve/cyl engine the camshaft is held by 5 bearing saddles, one over each pair of valves per cylinder. That design is the best as it holds the camshaft true to axis while the lobes are applying force to open the valves.
This design - also like suzuki G10 design is a very bad idea - specially on a diesel engine.
