If you sold it, it was your idea. That means if the buyer wants to patent it, you need to be cited as the origin. As far as I know, private discussion is not publication (which presumes widespread public dissemination). In addition, absent the public discussion/revelation anyone at all can think of this idea and patent it. Recent changes have muddied this with first to patent = the win.
Many companies intentionally publish inventive details to (try to??) place them in the public domain as a troll blocking mechanism.