I think you did all right, and did absolutely nothing wrong.

Because I'm an up-front kind of girl, often ride on my own, but don't mind sharing the burden of wind with other cyclists I meet on the road, I might have acted a bit differently from the start. After a kilometer or two I might have said up front "Do you want us to ride together for a while?" if I wanted to share the wind with him, and if he said yes, I'd say, "What about XYZ-distance-or-time relays?". That way it's explicit that we're drafting off each other and that none of us will be doing all the work. Maybe I would consider adding "If you want to go ahead just let me know... I'm taking my time/don't want to burn my legs I have a race tomorrow/am not very fit and wouldn't want to hold you back/etc."

That sort of exchange does create sort of an obligation (a mild one, mind you!) to stick around each other until one or the other clearly says "ok I'm dropping you" or the other says "you can drop me you know don't worry about it".

The short exchange also gives me a chance to gauge the skill-level of the other rider. I don't mind someone who's not fit, but I don't want to ride behind someone who doesn't know how to behave in a paceline. If I realize it's unfortunately the case, I will find a way to break our little contract.

I don't like drafting off others or having others draft behind me without explicit consent. Drafting is a dangerous thing, the person in the front has lots of responsibilities, so I need to trust that person, and the person behind me has to trust me. So I'd rather be clear on things.

But I'm a safety-freak.

Good luck on your training!!