A friend of the OP may be onto something 
Or maybe he is just very fond of the privacy+security combo.
In any case, I agree with you - if there is no illegal stuff in question, nothing would be a problem for a person not using XMR, but just BTC.
In my country, for example, there may be some legal problems if you use Bitcoin. So it would not be superfluous if I take slightly increased security measures when using cryptocurrency. Lately, something has even become scary. I do not want to end up under arrest because of these trifles. That is why it is necessary to use not only confidentiality, but also to protect yourself as much as possible. Or maybe he is just very fond of the privacy+security combo.In any case, I agree with you - if there is no illegal stuff in question, nothing would be a problem for a person not using XMR, but just BTC.