Yeah, I'm pretty sure he means that instead of evil omen dropping your resisting spells to a flat 50, like it always has, it will now drop your resisting spells BY 70, in order to scale with people's skills being over 120.
So for example, if you have 170 resisting spells at the time you're hit with an evil omen, it will drop you to 100 (a -70 penalty), instead of from 170 down to 50 (a -120 penalty).
Example 2: At 200 resisting spells, you would drop to 130, before, you could have 200 resisting spells and get hit with an evil omen, and it would still drop you to 50 (a -150 penalty, ouch!), which kind of made having any resisting spells bonus pointless.
Good idea, imo. Makes a use for all them +20 resisting spells red tunics ;P