oh-my-zsh turned on autopushd? How can I turn it off?

It's set in ~/.oh-my-zsh/lib/directories.zsh. I would either comment it out there, or unset the options in your .zshrc after loading oh-my-zsh.

Maybe you have the dirpersistplugin from oh-my-zsh loaded or perhaps you are sourcing some kind of $ZDOTDIR/z.* at startup. Have a look at the manpage for startup files.

Just type unsetopt autopushd to disable the feature for the current session and setoptto verify that it is really unloaded.

To find the source of the problem I would run zsh -x 2> log, exit immediately and inspect the context of every pushd in the log...