from the article:
"181 patients with SARS-CoV-2 pneumonia..."
These patients had pneumonia and were infected with Covid-19 for days prior.
Its too late for the hydroxychloroquine to stop the Covid-19 virus. The disease has progressed to its second phase wherein the virus and other opportunistic pathogens (e.g., bacteria) attack the lungs and other tissue. Antibiotics may help but these patients arrived too late at the hospital to gain the full efficacy of hydroxychloroquine, which when coupled with zinc sulfate, slows or halts the viral replication.
Based on this in-vitro study - https://www.nature.com/articles/s41421-020-0156-0 - if I hypothetically had both Chloroquine (CQ) and Hydroxychloroquine (HCQ), I would prefer HCQ for prophylaxis, but if I was exposed and likely infected or developed sympthoms, I would choose CQ. The loading time or HCQ is longer and it appears less effective at higher MOIs "the data suggest that the anti-SARS-CoV-2 activity of HCQ seems to be less potent compared to CQ, at least at certain MOIs."