I don't see anything in the original post explicitly promising any specific price. If anything, there's specific mention that the price is unconfirmed. SPG tried to be nice, maybe some miscommunication happened; however, I don't see any promise being broken.

Your response is likely a good reason for that team to avoid private deals in the future, with you or others. Pragmatically speaking, involving lawyers over a small miscommunication generally evaporates any goodwill you might have had prior to that point. Also, assuming that you're using your company's legal team, that's also probably a poor use of their time.