He's right. Packs you earn before new players are added can never include the new players. I had about 10 stacked up unopened a few updates back since (at that point) I already had all the players. Sure enough once the patch came I opened them all up to reveal exactly zero new players.
Worth pointing out that, at least on PS4, the latest update finally improves chances of getting new players. Rather than just being a 1 out-of-however-many-players-there-are chance i've seen every pack lately give me at least 4 new players. This has happened to me 5 times in a row now. One time I got 5 new players. So finishing out the missing players has gotten way, way easier.