Seems you only have a cut down version of that article.
Doesn’t the bottom bit bear out exactly what I just said.

What about all the test kits sold by China to other countries that have been proven faulty?
My friends explanation is that the level of antibodies (and he gave me a number like ‘less than one million particles per cc’ is insufficient to give a positive test. Therefore quite likely the discharged Wuhan people had false negatives and were not recovered when discharged.
Remember that those people were by and large vulnerable (ie elderly, pre-existing conditions etc.) which means by itself their immune systems were not working as ‘fast’ as they should.