XKCD isn't saying that four dictionary words strung together is as strong as a 30-character random password. He's saying they're better than an 8-character pass

XKCD isn't saying that four dictionary words strung together is as strong as a 30-character random password. He's saying they're better than an 8-character password which must include at least one upper case and one lower case letter, one number, one symbol, one loud bird call and one soft squirrel noise.