Most Helpful Guy
Your understanding is one meaning of 'friendzone', sometimes it is instead taken to mean that one person isn't attracted to another because they have had a platonic friendship for some time. That is had they not been friends they might well have found the person attractive, it's having been friends that renders the interested party unsuitable. I think it's plausible that this could happen, people who have grown up together often have an aversion to dating each other just as siblings/relatives do, it's not a huge stretch to suppose that some people may develop a similar aversion to seeing a long term friend romantically.
The thing is though, when guys use it on here it's generally just the case that the girl isn't attracted to him when they met.