The equation is wrong according to the other equations for neutral side chain and basic side chain if we keep in mind that the assumed values for pKa1, pKa2, and pKa3 are to be carboxyl group, R group, and amino group, respectively. So I'd suggest changing this because (pka1 + pKa3)/2 assumed we are adding the carboxyl group pKa and amino group pKa which is wrong

The current formula is correct as well as the formulas for calculating the pI of basic and neutral amino acids. The convention these cards are built on is that pka1 = a-carboxyl group, pka2 = a-ammonium group, and pka3 = side chain group. We made new graphics to make this convention more clear!