It doesn't matter if Merhawi told them there were no reductions. He could have told them NB were also throwing in a puppy and warm hugs. Berian's original Nike contract from 2015 stipulated that any offer from a third party would have to be submitted on company letterhead. Merhawi failed to do that, but Nike asked him to do so, and Merhawi complied.
Nike then informed Merhawi that they would match the NB offer, but that it didn't mention anything about reductions, so they wanted clarification on that too, but that they intended to match regardless. Merhawi never provided that (maybe he mentioned it in the conference call, but again, that all has to come on NB letterhead). He obviously could have gotten that from NB, since NB testified under oath that the deal had no reductions.
So why didn't Merhawi get NB to provide that? It's fairly obvious that, because Berian didn't want to be with Nike, Merhawi knew that providing such documentation would mean that Nike would fully match, and it would be over.
So why did Nike later send the full contract that did include reductions? I'm not sure, but I'd guess it was a means to force the issue, since it was apparent that Berian had no intention of giving in, and it seemed as if the communication dried up. I'm no Nike fan, and can't understand why they'd go to such lengths to keep an athlete who doesn't want to run for them, but if you look at it from their perspective, you can see how they would feel Merhawi didn't deal with them in good faith.