It's not an accent thing to be sure, especially as the two words are homonyms. These people are hearing the sound otto/auto and thinking a human was given the name "Auto". Out of necessity I do spell out my name most every time. I did so in the photo that started this thread, and you can see the server scratched out the incorrect "auto" and corrected it below that. Most recently I've just said "Otto" to see what they come up with. The elephant in the room here is demography. Every person who wrote down "Auto" was of the same background, one known for creative first names. The Otto vs Auto episodes are likely a cultural phenomenon more than anything else.