The general causes for a hernia as relates to this question include:
- Extra weight
- Heavy lifting
- Poor nutrition
While I'm not a doctor, nor do I play one on TV, I'll go out on a limb and say that the overexertion and heavy lifting required to cause a hernia are when it is above and beyond what the body is prepared to handle. If you have gone up in weights more quickly than you are really prepared for, then you might be in danger. Particularly if your core is not already strong enough to support what you are doing at the preacher curl bench.
Weightlifting belts are meant to provide stability in your core. It will compress your organs even more. It appears that the hernia is more related to the muscle tissue than the organs themselves.