Yeah, I agree with this.
I initially thought that they would explicitly mention that you would need to be enrolled full-time for at least two years in a PhD study. To my surprise, they said no such things, so it's better safe than sorry (and do NOT modify the template or the wording from their example of letter of attestation; even though it should technically not change anything, we never know).
I will try to look into OP6C later.
On a side note, I'm actually a bit relieved that they did not get rid of the PhD stream with the announcement of the new FSWP program (MI-8). The last third stream of FSW3, which was based on one's one year enrolment as an international student or as a foreign worker (under MI-1), was only there for about a year before they removed it.