Meddon,
Not sure what info you're after from your post.
If you suspect that one of your LB's is not purebred, then it is perfectly possible to cross any pig with any pig, so yes your LB could look like an LB but actually be a cross. And of course the boar could have been a cross breed looking like an LB, or the boar could have been any other breed. If you think this is the case, check back with the breeders. Crossbreds can easily look like either one of the parents. I would not expect two LB's to throw anything but a black pig, but maybe LB experts out there know different and it does rarely happen?
We cross tamworth and saddleback, and as HM says they throw a quieter pig than a pure tammy.