Given that this compilation was published on March 11th, and hpmor finished on March 14th, I don't think it's making the rounds now because of the timing of hpmor. Their finish/release dates are simply close together.
I think it still may be - people are posting this around as an additional reading for those who liked HPMOR; number of people who read that fanfic is most likely much greater than the number of people that read the Sequences.
The release dates were purposefully close together.
I don't have inside knowledge, but yeah, it seems extremely likely -- the sequences have been available for years, after all.
They didn't wait for the end of HPMoR to publish this book - they made an extra effort to have it ready in time!