He didn't say he was a hermit, he just said he only ate out once a week! Perhaps he likes to do sports, or hike, or has hobbies or whatever - does not seem very friendly to be so rude to the poor guy!
HOwever, OP, some points you may want to consider. A small flat may have limited kitchen facilities - in many HK flats there is no oven for example - which is why many people eat out alot. Having said that, if you eat local food, eating out is no more expensive than cooking for yourself.
Aberdeen is a much cheaper place to live than the north of the island so you should be able to find something small and cheap there, yes.
If you live near your office, transport costs would be very low.
You will need to factor in electricity bills - the more time you spend in the flat, the more aircon you will use which can add up, but not that much for a small place!
You may want to travel around asia while you are here, you might want to think about those costs.
You will pay around 1000hkd per month in MPF and you have to manage your own tax - will need to save up for that at the end of the year. Can be complex at the start.
You will need a deposit etc for the flat, so need to have that ready.
Yes, you should be fine. Have fun!