Practically speaking, an HR department is usually constrained to considering candidates in comparison to a job description one or two levels of interpretation and rewriting removed from actual needs, or even more so in a large company. (In fairness, it sounds like the manager you have been speaking to is also not comparing you to specific openings, but rather to a general sense of the types of work being done in the company overall.)
Given all of this, any opportunity for a conversation with someone managing actual daily work is a good thing, even if that work is only adjacent to that which you actually want to do.
While it is possible that this person might be able to "sell you on the fit" of the specific role identified by HR, the more likely outcome to hope for is that you have a pleasant conversation and come to the mutual agreement that you are an interesting candidate in general, but for a different sort of role. Hopefully, this person then becomes a second informal champion for you within the company, and may forward your resume or casually mention you to a different manager who does have a need for someone with your capabilities, or a budget to staff a "new ideas" role not tied to a specifically identified business need.
One thing you may over time notice in the world of business is that while technical people often want to speak about a specific topic (and avoid sinking time into things unrelated), those in sales and especially independent recruiters often seek connection and conversation without heavy evaluation of the proposed purpose, in the hope that once a conversation is begun, a fit may be identified - or if not immediately then as an idea to be kept in mind and contact to be kept on file in case a possibility is identified in the future. This can be annoying if you are on the receiving end of irrelevant outreach, but if you are the person seeking to do business with a company and they offer conversation, learn from the prime directive of those in the sales role, and accept the opportunity to talk.