Before - or if you do it after make sure to subtract the effect of the sugar.
On the other hand, it isn't a really significant difference either way. 4 oz in 5 gal would add 0.0023 SG.
That's about what he measured, so the difference was probably due to measuring after adding the sugar. The standard 5oz that comes with kits is almost exactly 3 points in 5 gallons.
Of course, when you disregard the priming sugar, you're ignoring the extra alcohol produced. On the other hand, you also have to take into account the dilution when you boil the sugar in some water. The bottom line is, you're just making an estimate, so relax