It's possible the text being displayed is the text configured in CBSubs > Settings > Display > Plans.
Also, is there a way to disable the first tab (in tabed registration) at all when the plan is called directly. This would make more sense because the plan is selected as default and it gives more freedom to design custom registration pages...
Don't understand the question. You've CBSubs as your first step when using step by step from CB Conditional and you want it to disable when only 1 plan is shown (access by URL)? No, you can't do that.