You can assume they were seriously sick with COVID beyond anything a flu or cold is likely to do. We know that this means either anosmia, difficulty breathing, and low blood oxygenation, with viral pneumonia visible on X-Ray.
None of these symptoms that characterize COVID serious enough to require medical attention, more than what one would expect from a bad flu or a bad cold, are compatible with the report citing symptoms consistent with seasonal illness.
There are two other possibilities.
One is that they had seasonal illnesses that were serious enough to require some medical attention, but not COVID. This is consistent with the report, and not implausible. This is just as possible whether they have similar attitudes towards medical attention for seasonal illness as other staff.
The other is that they had seasonal illnesses that were not very serious, but sought medical attention anyways. This is expected to happen if virology staff have similar attitudes towards the issue as the rest of Chinese society.
No matter which way you slice it, there is no indication they had COVID. Even if you remain ambivalent on their behaviour.