Pneumonia is a diagnosis (well, class of), not a symptom nor a sign, which are distinct terms of art. You can have pneumonia that shows up on a chest X-ray (a sign) without any symptoms.
A better example might be high blood pressure, which many people understand can be silent/asymptomatic for years but is easily measurable.
Point still stands, symptoms are noticeable and reportable by the patient. If covid gives you pneumonia you may still be asymptomatic.
Your post is a bit confusing, I'm not exactly sure what you're arguing. Walking pneumonia (which is what you're describing; the term of art is atypical pneumonia) is extremely rare, and it's not what we're talking about here. Non-atypical pneumonia has symptoms, ergo is by definition not asymptomatic.
Your (uncited) claim that "These patients have low oxygen because of COVID pneumonia." There are plenty of sources out there[1] that talk about a strange, again, leading indicator, known as "silent hypoxia" which has nothing to do with pneumonia. Further, there's a lot of confusion in your post: if COVID ends up giving you pneumonia, you are definitionally not asymptomatic.
[1] https://www.lung.org/media/press-releases/silent-hypoxia-cov...