There was no intentional tap.
It's extremely common for a "phantom tap" to occur in a situation like that. The man being choked (and beaten, in this case) is reaching with his trapped arm to find his positioning.
People who don't grapple/wrestle don't realize that a trapped arm doesn't move the way the brain expects it to move, so a "tap" can occur when there is no intention of tapping.
Note also that Borshchev showed almost inhuman toughness in this fight and previous fights. The idea that he would then tap to a brabo choke that wasn't yet properly finalized is dubious.
Source: this happened to me 16 years ago in competition, but the referee was superior to Keith Peterson. The other guy's corner started claiming I tapped (I didn't). Eventually I was able to escape and submit my opponent.