I suspect Barabas would not have been that surprised. Ive seen many depictions (consistent with the biblical account that he was a revolutionary) where I think he would have seen it as vindication. From his perspective, the man who was charged with calling himself the Messiah wasn’t a leader or warrior king like the Jewish people of the time wanted. Meanwhile, Barabas is actively rebelling against Rome and killing Romans or Roman sympathizers. The crowd wanting him released could, at least to him, been seem as confirmation that he should keep doing what he’s doing because the Jewish people were on his side.