Character Reference Letter

A doctor I've recently met (through very random circumstances) has begun to mentor me, and we call every week. He did his residency at my dream school and hearing his life experiences and advice is really incredibly insightful.

He's offered to write me a Letter of Recommendation, and he described its purpose as being a character reference. He says he writes them usually for med students applying for residency, but says he would write it for my med school application.

Is this normal, or even advised to accept? I fear I might be seen as trying to enter my dream school purely through nepotism or something, even though this doctor and I have no relation like that. I am unsure if I should actually accept his letter and send it with my other letters or just thank him for offering but decline. Our time spent together is purely him advising and talking with me, and we have done no work together in any capacity.