Earth is important, ask your contractor to correct it. And make sure he actually add back the earth not putting a dummy earth wire.

That make me wonder, is he tapping from another power socket or direct from Circuit box?

Yes, If you are sharing, you risk burning the internal wires. Electric hob can go up to 4000 watt and more depend on model, and normal 2.5mm wires won't be able handle that load.  If you loop you need to know what is being shared, some house share same wires for few socket.

You need to know your Hob max current requirement, and its recommendation wires size.

Assuming you have hood too, and from your information, I assume he also loop the same wires for hoob.

Good luck.

Opps, sorry. Hood not so much concern on power drawn.

You must also take into consideration the type of hob. If it is gas type, you need to mount it higher, if induction, you can mount it lower. So read your hob's instruction about how high to mount the hood.

for example, my hob's instruction says "to install 65cm from lowest part of hood"
and my hood's instruction says "install hood not lower than 50cm if using electric hob, and 65cm if using gas hob"

so for my case, if I am using induction, the hood can be as low as 50cm
if gas hob then, 65cm, no lower than that.

installing a bit higher doesnt posed any problems other than maybe a drop in efficiency

follow the manufacturer's instruction is best.