Excessive radiator fluid temperature is common message which come during start when there is no enough voltage from battery during start procedure (at least seen by ECU). Sometimes comes up also with ASR/VDC/HH errors.
Remember that diesel first (even in warm temperature, but shorter), after you plug the key, warms up glow plugs - and that indication on the dash is not really showing the real glow plug heating time (it depends on temperature, and may be like say even like 15 sec in low temperatures) - this is high current load - changes from aroudn 50A at first second to say 30A after glow plugs become hot, and lowers voltage seen by ECU and other computers.
I suggest you start from simple thing - 15 minute job you can do yourself - clean up ground lead connection from battery to car body - the point at car body gets often oxidized and this may be reason of a lot of electrical "funs" in our alfas. Also, clean battery clamps.
Do you have battery charging working well? W.g have you measured it during engine is running - should be more than 14V if I remember correctly (with lights on etc).
EDIT. One more what I coudl think of, is starter already in poorer condition. That could be case in car which has on the clock over 200kkm as I see on video you posted. Usually it is just dirty, maybe starter brushes are used etc, and it is not that effective anymore, so uses more current, does not spin so well as it should, so starting takes more spins and time, and that manages to weaken battery output after a few seconds and cause enough voltage drop to end up with various errors shown on the dash. As far as I know, standard refurbishing of starter cost in Poland is order of EUR40 (includes stripping it to small pieces, cleaning, changing brushes, repainting case and some other required maintenance and testing), so if cleaning of ground connection point and battery terminals, and checking if charging is good, you may consider looking at starter. You may also check other GND/+12V connections between battery/body to engine/alternator/starter.
Last edited by epsonix; 10-11-16 at 20:23.