Just because one company claims that their "Tetra L Superb" is a hybrid, does not make White Leghorns a hybrid.White leghorns are considered to be hybrids.
They are sold as hybrids.
It is a real fact that hybrids are crossbred and commercial leghorns are outbred.
They are created from an ABCD system.
See the picture on the following link:
http://www.babolnatetra.com/uploads...mmercial_Hybrid_Management_Guide_2016_ENG.pdf
White Leghorns breed true and therefore are not hybrids. Different companies are making claims that their particular line is different as a marketing tool. They really don't care about telling the truth when it comes to something that they think benefits their sales.
Red Sex Links and Black Sex Links are hybrids because they are created from two different breeds of parents and they will not breed true. White Leghorns are all the same breed even though there are different lines of them. The slight differences in the lines do not make them a separate breed just as outbreeding or crossbreeding those lines does not make a hybrid.