Reading the scale they developed, I'm not sure how one could distinguish their results from the more general bias that the majority of people believe they are above average at any given thing (especially with statements like "I do X better than other people"):
In the link you provided, I didn’t see any formal validation studies presented justifying the scale/test/instrument they were using here. That’s the sort of practice that leads to a inability to reproduce and validate the results...
https://onlinelibrary.wiley.com/doi/epdf/10.1002/ejsp.2721