I wasted 2 hours to figure out why my newly created taxonomy field is showing the input as row based instead of 1 line. I was comparing the tags field of the Article content type. Checking the taxonomy vocabulary. Trying different combination of settings.
What I want is.
Lo and behold, the culprit is setting of the form display widget of your field. It is located at Manage form display tab of you content type. Set the widget of your field to Autocomplete (Tags style).