I agree, after this happened to me I learned of a few other situations where the same thing happened to other friends.
On my end if was a mix of naivete and flattery which made me want to take the meeting. I suspect it is the same case for others. I will not make the same mistake the next time it happens.
Well your license is only as good as you are able to enforce it. Even with the law there is no guarantees.
I grew up thinking that people would follow the spirit of open source rather than the specific letter of the law. This is obviously not true, and probably never has been.
No license stops someone from spinning off an OSS project into their closed-sourced enterprise offering. It's just sad that most corps see nothing wrong with this