Was he maybe not just referring to the vexes, thus those small, flying mobs around evokers? I mean, the hinted turtles in 1.10 1.9 also became indeed mobs with shields around them, namely the shulkers.
I think Jeb knows what a bird is. I'm pretty sure when he says birds are overdue that means birds, not vexes
I'm not saying he doesn't. And he also probably knows what turtles are. But still we have shulkers instead of turtles in 1.9 (not 1.10, misstake on my part). So it is still possible he is trolling a little bit about the birds.