According to a recent article in Psychology Today, the power of first impressions is undeniable and «first impressions matter, for good and bad» (Google «the halo effect» if you're curious and want to learn more about
the lasting power of first impressions).
As for the effect of confidence on perceived ability even after actual ability has been reported, the authors note
the lasting power of first impressions have been long known to disproportionately affect our judgments of others.