Scores are unnormalized. Dividing by the sum of the shown scores produces exact posteriors that sum to one, then the larger posterior gives the exact argmax.
highlighted = computed this step
Normalize the scores
The denominator is 1/4 + 1/12. Dividing each score by that sum gives posterior A 3/4 and posterior B 1/4.
P(A∣x)=3/4,P(B∣x)=1/4
Why the sum check matters
The rendered table shows posteriors sum = 1. This is an exact check that the normalized fractions form one distribution over the shown classes.
P(A∣x)+P(B∣x)=1
Summary
The larger posterior is A, so the exact argmax is A. The renderer recomputes that argmax from the displayed count table.