Balaji Srinivasan had a medium post about this:

https://medium.com/@balajis/peer-review-of-covid-19-antibody...

A summary of his post:

1. There were 2 false positives in 401 pre-covid samples (known negative). Assuming a normal distribution, 2 sigma confidence can account for up to 80% of the positive results reported in this study.

2. For the virus to have already infected this many people, it should’ve spread so fast that it doesn’t match what we know about similar epidemics.

3. The researchers recruited volunteers via facebook ads. There could be sampling bias here.

I encourage everyone to read the article: my summary < The original article.