The ASPCA says Boston ferns are non-toxic to cats and dogs, but of course does not mention lizards. Given that Boston ferns are not known to be poisonous, I would think he is probably safe unless there was some kind of Miracle Gro or something on the leaves. Keep an eye on him, give him lots of water and watch his behavior closely, and take him to a vet immediately if you see anything out of the ordinary. You could also call a reptile vet and ask them just to be sure.