chmod to make some scripts executable, and now my bash shell is tab-autocompleting all available commands.
How can I make it go back to completing just files / folders in the current folder?
It always tab-autocompletes command names as the first thing after the prompt. Are you saying that even after you enter a command name, it keeps offering command names as the next word of the command line? Are you sure you're not in a directory full of command files?