Assuming that you are in Ireland, to comply with Irish wiring regulations as per the ET101:2004 (And amendments) the hood should be connected as follows:
Option (1)
You can connect the hood using a plug and socket. The socket can be installed near the hood in a location where it can be accessed i.e. you can't cover it over with kitchen cabinets. However, you can install it in a cupboard.
The plug should be a standard IS401 (BS1363) 3-pin 13-amp plug carrying a fuse appropriate to the particular hood you have installed.
Option (2)
You can connect the hood via a fused switched appliance connector unit connected to a normal socket circuit (i.e. typically a 16 or 20amp radial in Ireland).
The fused spur should be protected with an appropriately rated fuse for the appliance e.g. a 3amp fuse in this case.
The appliance circuit supplying the appliance must be protected by at maximum a 30mA RCD regardless of which way it's connected.
Those are the only two options that should be used, wiring the appliance directly to the back of a socket is illegal under Irish regs.
For neatness of installation I'd go with the fused spur option.
More than likely, your electrician would indeed 'tap' into a socket circuit but he will connect the appliance via a fused spur, not just directly into the back of the socket without local over current protection. I think that is the junction that is depicted in the diagram you linked.
Also, he will have to run an earth to the connection point anyway, even if the appliance is double insulated. So, he'll just use standard 3-core cable.
Irish wiring's a little different to the UK in so far as we tend to use 16 and 20amp radial socket circuits rather than the 32amp rings that are common in the UK, but very similar rules apply for connecting fixed appliances. They have to be locally fused and have an isolation switch, otherwise they need to be connected via a plug and socket.
Aluminium tube wiring is used in the USA (required by some states only) because of the type of construction they use in their homes i.e. they use wood. It is highly prone to fire. Irish, British and most European construction uses plaster and concrete. Electrical wiring is typically buried in ducting in the plaster. This is extremely fire-resistant.
Also, the use of higher voltages in Europe tends to mean that wires run less risk of over-heating. (Ohms law). 110V circuits overload much more easily and run very hot if they do.
It also means that relatively low powered circuits in the US and Canada require much bulkier wiring than their counterparts in Europe or other 230V countries.
Anyway, aluminium tube wiring is not required for your cooker hood in Ireland.
