Don't get stuck on titles. Focus on the things that matter.
If specific functions or roles are important to you, then yes - now is the time to clarify. If a specific salary or career path is important (getting more in to coding vs more in to leadership), then clarify now.
One company's "architect" may well be another company's "senior" or "lead." You need to clarify what those roles mean to this firm, and potentially clarify why they're offering you the role they are.
Most interviews include an opportunity for the candidate to ask questions. As a hiring manager, it's staggering to think about how few candidates bother preparing or asking anything beyond one or two throwaway questions. They're giving you a chance, use it! If you're beyond that part of the process - and it sounds like you are - you can still reach out to the recruiter, hiring manager, or whomever you're working with to clarify.
Good questions are things along the lines of,
- Can you walk me through a day in the life of X role at your company? What sorts of activities will I be focused on?
- What other roles or people within the company will I work with? How will I interact with them?
- As an X role, will I be more focused on A, or B? (Coding, vs leadership? Architecture vs hands-on development? etc.)
- As an X role, will I be more involved as an individual contributor, or more as a leader/mentor for others?
Their responses to these question will give you a much better feel for what the titles actually mean, which will put you in a better position to respond to their offer.
If it turns out you do think they're offering you something you don't want (either because you wouldn't be good at it, or because you just don't want it), again, now's the time to ask.
Be very careful though, as insinuating you're not interested, or not a good fit for, a role they're offering is as likely to result in no job, as it is to result in your dream job. Employers generally view recruitment as filling specific positions and not as finding a way to hire a specific person. If you want X, but they only have an opening for Y, they may simply pull the offer from you and go find someone who actually wants Y.
That, combined with the way you present this as a bit of a bait-and-switch situation, gives you a chance to ask an innocent question to test the waters:
I understood that I was applying for X, but you're offering Y. Can you explain what the differences are, and why you're offering Y?
Perhaps they've already filled X and are trying to fill Y now. Perhaps they have both open, and they think you'd be better at Y (despite your reservations). Perhaps there was some sort of simple mix up, or perhaps the position isn't even well defined within the company and different people call it different things. The only way to know is to ask.