"Having one item missing or low in one market is a food shortage?"
NO and No.
Not in one market, which is why I asked you what was happening elsewhere.
And not one item. And certainly not beer and kettle chips.
As we often say: This is Thailand!
When my GF last discussed food, she mentioned that she had stockpiled noodles, rice, eggs, and pork. She said nothing about beer and kettle chips.
At her Tesco Wednesday there were no noodles, rice or chicken eggs (they had duck eggs, which she doesn't like).