That said, I am a second language English speaker and haven't even completed English as a second language in high school.
The original spellings of the verb forms are dis, dissed, disses, dissing.
I think it's only normal for people to end up spelling it 'diss', especially as the original word it was derived from becomes less known.
True, but you'd think a publication like NewScientist would strive for (some sense of) correctness in terminology selection.
Also see: http://www.grammarist.com/spelling/dis-diss/