Depends, Artemis mentioned that this was probably done with a library code hitting HF and others, now if all those others are hobby related it's somebody with an interest. But I would assume its more likely its all smaller E-commerce websites.
No, this doesn't have to do anything with the real HF site being hacked. You can create a spoof site without ever compromising the real one.
They may have got the email addresses from the hack, but non-customers receiving the emails suggests some other source.
The biggest issue is creating the emails so that they contain all the right names and logos. Note how the PayPal scam emails always address you as "Dear Customer" instead of by your name like the real ones?
It takes at least some effort to create site-specific scam emails. Someone usually going after CitiBank and PayPal customers wouldn't find HF worth their while.
Hmmm... it might be possible to exploit a hole in a popular eCommerce software to extract enough accurate information to automatically create the scams (correct names, company logos etc.) But then you should see multiple scam sites hosted under thepromo.link -- I can't find any. That would mean that either they rotate the scams in and out (slow for small gains) or actually register multiple domains for scamming (expensive).
The entire point behind these scams is that they are virtually free to run. The returns are low, but it doesn't cost anything to try and with enough volume you can earn something. Actually sinking money or effort into them makes them non-profitable.