These two words are often used when someone is advising you about securing your bitcoin investment, but thinking about it, the context may be misunderstood clearly by people in different situations who nor really understand well.
I never really reason the two words having a different meaning but as I look up the words for online just now I come dey understand the difference although both words dey very similar and both has to do with withholding information from people.
From within I read, privacy na say you decided to hold the information for yourself while secret na say you no want make people know about the thing. So if you don't want people to know about your Bitcoin holdings na secret you dey keep so and this might involve you not telling your family because you no trust them.
But in the context of Bitcoin, I think both words can be used and doesn't have any difference because when you hold the information from your family, you're keeping your privacy and being Secretive at the same thing.