Looking at past results, it's reversion to the norm. Don't read too much into it.
Having said that, recent Labour results in byelections for the valley authorities have generally been poor and in some cases pretty dreadful. So whilst I did have a sneaking suspicion about this one, its not that surprising nobody actually went for a Labour win in the prediction competition.
Good news for Labour to have a gain, but hardly unsurprising.
I don't take part in the prediction competition to save my own blushes, but 2017 did stick out like a sore thumb compared to other elections as it was a combination of bad year for Labour with strong candidate.