That was not remotely the same woman.

TIL most people think Ted doesn’t have a Southern accent. Could’ve fooled me! It’s not Deep South, but I spent several years in the Midwest (Nebraska and Iowa) and almost everyone I met had a neutral accent, which Ted’s isn’t.

Anyway, to give a potential answer to your question — the actress who plays Ted’s mom, therefore presumably the character as well, is from Kentucky (no info either way on Ted’s dad). So even though Ted grew up in KC, his household would’ve had a Southern accent influence, which he easily could’ve picked up.