There's a good explanation of the legalities of the deal here:
http://business.financialpost.com/news/fp-street/warren-buffett-is-not-the-only-winner-in-home-capital-deal/wcm/cb03e263-8028-49f7-b588-0aebc8252fa4
The "discounted" share price was agreed upon 10 days ago, based on a five-day rolling price. The fact that the stock has risen since then is just gravy.
Anyways, back in early May, any one of us could have bought HCG on the open market for about $6/share - even better than Buffett's price. "Those who dare, win."