I mean, getting an email like that is bad, but it's better than not getting an email like that :D
Last year a huge game company released something built on my tiny open-source game engine (uncredited), and I only found out about it later from a kind internet stranger. All things considered, better to know in advance so you can at least have your own response ready, so you can comment in the relevant HN/reddit threads, etc.
That said, the "keep it secret" part of the mail here does sound weird, but given the other history there may have been an NDA in place.
Last year a huge game company released something built on my tiny open-source game engine (uncredited), and I only found out about it later from a kind internet stranger. All things considered, better to know in advance so you can at least have your own response ready, so you can comment in the relevant HN/reddit threads, etc.
That said, the "keep it secret" part of the mail here does sound weird, but given the other history there may have been an NDA in place.