I thought the same as you did. But when someone cited Hoovers Olive Eggers, I checked what their website said-- yup, they're using Cream Legbars in some of their lines. Cream Legbars are the obvious source for a crest or tuft on the head while also providing a blue egg gene.
Huh?
https://www.hoovershatchery.com/oliveegger.html
Hoovers Hatchery Olive Eggers. A quote from their description:
"Our Olive Eggers come from a couple of different crosses. We have one line that is a cross of Americanas and French Cuckoo Marans.... We also have another cross that is between...
You gave the short form, that makes perfect sense to people who are used to sorting out matters like this.
Then I pretty much said the same thing, but with a lot more words :D
I agree that it must come from an Olive Egger mother if it hatched from an olive egg.
If the Olive Eggers have single combs, then Olive Egger x Orpington would give chicks with single combs. That cross would only produce chicks with the usual number of toes (4 per foot: 3 point forward and one...