Sounds like a legal question. Legal has nothing to do with right or wrong, It all depends on who has the better lawyer (legal team)
Realistically, (My opinion) virtually all catastrophic muzzleloader failures are user error ( bad loading/barrel obstruction ) Sure theres a lot of blown guns out there, but muzzleloaders are basically hand loaders without case limitations, and more steps involved to load, hence more chances to get it wrong. Short started projectile, double load, wrong powder are probably the most common. Everyone has had a dryball, its known to be common. but the scary ones usually dont get circulated as readily. Focus and witness marks are key.