Do you think dumping someone because they're dumb is valid?

My boyfriend and I were talking and the girl he dated before me came up. I asked how did they end up breaking up. He said "How do I say this nicely." I told him to just say it and he said "She was.... Stupid... So stupid it was embarrassing." He said when they were together she got fired from her job and she was supposed to be job hunting because they both paid bills and that she would refuse any job that paid biweekly because she believed that if you are paid biweekly you are getting paid less and scammed out of 2 paychecks. She was in her 30's btw. He said he tried really hard to explain to her that's not true. You make the exact same amount you're just paid at different times. She wouldn't listen and would get mad when he was trying to correct and explain it to her. He eventually decided she was dumb to a level where you can't function properly in the real world. I don't think I've ever dumped someone because I found them dumb. Do you think that's shallow or would you do the same?