I've seen something like you mention in vscode for snippets - that is fixed pieces of code with some variables, and the IDE skips to them w/ tab, so that you can fill in the values. But that's only for already made snippets, afaik.
The tab autocomplete in cursor is more of a "next action autocomplete", wherein the LLM (a 70b fine-tune from what the team said) will "autocomplete" the next action that makes sense in context. Imagine changing something in a fn definition, and then the cursor jumps to the line where you used that fn. I'm sure something like this example could be hardcoded in an IDE, but this works ootb in a general way.
Not AI, but it was nice to have back 10-ish or whatever years ago.