First, I'd want to have a better idea of what was actually in that egg. I see folks post all kinds of things on here they think are in the eggs, then when they post a picture it's just a meat spot or something like that. I'm sure you can't get a pic or anything at this point, but I'd personally not treat, cause I'm not into giving potentially harmful medications when they're not needed. I'd ask your customers to please photo anything funky they see in an egg so you can monitor your chicken's health. Your customers want eggs from healthy hens!
If no one else has seen a worm, and you don't see any in the poop, and your birds are in good condition, active, glossy feathers and eating well, I'd just consider it a one off and continue to monitor your flock like you always do.
This is what I was going to point out...it could just be a meat spot, or extra chalaza(? I think that's what it's called), the white stuff attached to the yolk. If you just heard it from a buyer, they might not know what they are looking at.