He's not being negative on things but commenting on his bounty findings and whether we will be implementing other improvements and fixes as suggested by the MTP authors. mrb's submissions are valued.
His main contention is that @hidetoshi had previously criticized Zcoin for not making the submissions to the MTP competition public straight away and felt that we weren't being transparent. Our reasoning then was that we wanted time to verify such submissions before making them public. However since MTP is only on testnet, we accepted the criticism and decided that transparency is more important and have been making submissions public here: https://github.com/zcoinofficial/zcoin/wiki/MTP-Audit-and-Implementation-Bounty-Submissions
Hidetoshi and I have since discussed this in private and the misunderstanding was cleared up and we are both in agreement that collaboration between teams should be encouraged and sharing submissions facilitates this and have since been in communication. Hidetoshi represents a group of 14 scientists of which Fabien Coelho is a prime researcher with regards to PoW mechanics.
Hidetoshi has not formally made a submission to the bounty yet. However he had kindly offered to share his preliminary draft findings with us so that we can assess our own implementation to see if it has any exposure to the peer reviewed threats. The paper he submitted has been very helpful but is still in a draft form though I believe he will be making it public shortly sometime in the next week or so after finalizing it and getting feedback from the MTP authors. I personally don't think there is any issue in this in making sure that the paper is in a good state before releasing it to the public and as the draft was extended to us in goodwill, we greatly appreciate it. Once the paper is released, we'll also put it up on the github.
That being said I think both hidetoshi and mrb have the same aim, which is to contribute to the betterment of MTP and also get a share of the bounty which is what the bounty is for and we value both their works greatly.