I didn't see any mention in the article about memory T and B cells. The article only mentions antibodies. Where did you see this?
Upon infection or vaccination, your body will also produce antibody-producing memory cells to help respond more quickly if you are infected in the future. If you want to test for these memory cells, you can't use antibody tests. You have to use specialized tests that look specifically for the memory cell responses.
There are some commercially available tests, such as https://www.t-detect.com/, which looks at the T cell response.
A lot of the commercially available antibody tests will fail to detect a prior infection after just a few months. T-Detect now says that its test can pick up infections that occurred 10 months ago. 10 months is probably not the limit of detection; it's just based on the amount of time T-Detect has been available to the public.
Researchers have found memory T cells that respond to the original SARS-CoV virus 17 years post-infection:
In the months before I was vaccinated I had on two or three occasions something that felt a bit different from the usual cold/flu/allergies that I get, but was not severe enough to justify trying to get a COVID test. I'm curious if I actually have had COVID or not.
It's like saying "All people run out of edible food (antibodies) within hours of being hungry (exposure to distinct protein)". Well, yes, but we have the ingredients to make them in the fridge (memory cells). Just measuring the amount of cooked food (antibodies) will tell you how much I can eat right now, but I'm not going to starve (get sick) in the absence of the cooked food (antibodies) since I have the tools - raw food (memory cells) in case I get hungry (exposed again).
In the case of this study, they tell us we've run out of cooked food in 6 months. That doesn't tell us whether we'll starve, because we could have hella stores in the pantry and they specifically did not measure any of that.
https://www.nature.com/articles/d41586-021-02260-9
When you encounter the virus again, those with a healthy immune system will ramp up antibody production.
This is a very misinformed statement as this data hasn't been collected yet.