Writing complete fail on so many levels, it makes me angry that this game was praised for good writing. "You seen my dad, older, brown haired guy?" You mean, like, the 20 in megaton alone? "I fight the good fight with my voice kid, you better believe it!" "Intelligence: Ah, so you fight the good fight with your voice." "That's right kid you're just a chip off the old block aren't you." So my dad is functionally retarded, that would explain why he left me in a vault with a murderous megalomaniac without telling me he was leaving.
Just a note, if a kid in a vault suit walked into my hypothetical post-apocalyptic town, and asked me where to find his or her Dad, and an older gentleman in a vault suit had just recently come through town, it honestly wouldn't be hard to put two and two together.
Three Dog was being very vague from that point, and it's not like that choice required 10 Intellect.
Oh and yeah, even if he had known that the Vault Overseer was an insane sociopath, I think he'd still have to seriously think about leaving you to deal with him, or dealing with the plethora of brutal monsters in the radiation bathed wasteland outside the vault.