Good for you, and hopefully you are getting lucky on other casino journey. Well done, stay on casino who give you big wins maybe mentioned it would be great as well.
Better for him to stop gambling completely because he may get the same experience in other casinos sooner or later, sorry to say but as gambler we should be ready for all the worse possible case.
I guess it was a bad timing for him to do the bonus buy. I don't know how much he has lost there, but the losses might have hurt him very much and he wasn't prepared to lose the funds. This is why he is saying those here. Let's stop mentioning him, it will help him to forget about this thread and the unexpected loss. Most of the gamblers have the experience of losing like that either in Stake or in other casinos.
First, in my opinion, I think mentioning him is a way to talk sense to him, some people need some bitter lesson before they can wise up in gambling. Gambling is not where you should be desperate and risk senseless, so as it hurts now, he might be forced to "turn a new leaf" and gamble responsibly. Secondly, I don't know why gamblers are not sincere to themselves, did he think the same would not happen with another casino? Stake is not the issue, gambling is what it is and if you do not plan well for it psychologically and budgetarily/managerially, you will have yourself to blame for it.