Being more of a sprint race, it is not uncommon to have teams separated by only a few milliseconds. Add to this the known bias with the Regatta race course, many factors come into play when deciding who takes home the gold. Notwithstanding, the strength and coordination of the team remains a crucial factor.
As such, it is premature to guess if a team or another will become a black horse (or otherwise) just because they came close during a previous race. The most important thing is to focus on each race as it is. Otherwise, problems like complacency, or, if we look at the other end of the spectrum, unjustified fear, will compromise the performance of a team.