Swedes can get a visa waiver automatically within a few minutes online by using an online form.
ESTA is not entirely automatic. He could have been denied it; in fact, he probably will be denied it the next time he tries to get the ESTA, if he ever does. He will then have to go through the non-waiver visa procedure.
However, you only have to renew ESTA once every two years, not every time you fly. The DHS might have "discovered" whatever they discovered only recently.
He's Swedish national, just needs to fill in the ESTA, no visa requirement.
He probably does not need a visa (that's the case if one has a biometric passport)