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I used a sentence from the article as the title since I felt it represented the actual issue better, let me know if I should change it.
Essentially, Snap Store has basically no restrictions on publishing new applications, allowing for scammers to impersonate legitimate applications. In this case (and several times in the past) the target was a cryptocurrency wallet, resulting in ~$490,000 worth of bitcoin being stolen.
The "Safe" rating reminds me of this xkcd:
(For comparison, it seems being proprietary is an automatic unsafe rating for any application, which could be considered too extreme in the other direction.)
Another thing that they do that should make the process less vulnerable is they try to get developers involved in packaging their own applications (and have a verified badge, though I'm not sure how rigorous their verification is).