The article is a mix of half-truths and speculation with a few random facts sprinkled in. It doesn't represent any sort of scientific consensus. Don't take it too seriously.
Infections with typical rhinoviruses and coronaviruses build adaptive immunity to those viruses (as well as those that are genetically similar). This typically reduces the severity of subsequent infections. They didn't stay around for years.
When we talk about things that "strengthen" or "weaken" the immune system that's really an oversimplification. There's a lot more going on in the complete system.
