It's frankly a very easy trap to fall into when trying to discern why and how the nice guy archetype functions under a wrong paradigm about females, and, well, humans in general. The "friend zone" is yet another popular way to describe women as holistically reactionary individuals, which, though not really the meaning of what a friend zone is, is yet another example of how these expressions are kind of really bad at expressing what they really mean. I've "friend zoned" some people and it definitely was a very different thing than how the expression is usually used in these discussions. It's a messy bunch of words and it gets a bit tiring, honestly.
As for the topic in general, i think it's fair to say that i've gone through my own, though short, period of mistaking that feeling of wanting to be nice as a sign that i was in love with someone, which was fairly confusing for a couple of months because it obviously wasn't a correct reading of things, but i'm well past that nowadays. Now i feel like understanding how obvious it is that being nice and transmitting happiness is just yet another facet of how to live a good life was perhaps one of the great lessons in life that i've had the luck of learning. I feel like the one thing that irks me the most in "nice guys" is how stupidly provincial their understanding of humans, and life in general, is. It's sad, really.