Avocado flowers first open as female then close and open up again as male. This is why what your friend said is a bit strange because I would think that it isn't possible for an avocado flower to just skip the female stage. When it comes to when exactly these flowers open and close, there are 2 types - A and B. With the A types, the flowers open up as female in the morning, then close in the afternoon and then open up again as males in the afternoon of the next day. The B type flowers open up as female in the afternoon, then close down and open up as male the following morning. This means that in their natural habitat, you will have an overlap between type A and type B trees, where one type will have male flowers and the other female which essentially allows for cross pollination.
According to a source I found, this dynamic is a bit disrupted outside of the native range and it can happen that there's overlap of male and female flowers on the same tree, essentially making it self-pollinating, but apparently this can only be the case with type A while type B can never be self-pollinating. Now I haven't confirmed this so please take it with a grain of salt.
I can tell you that I found a Mexican avocado tree in my hometown of Bar, Montenegro that looks like it's at least 10 years old and that blooms every year heavily but never sets fruit. When I went to check the flowers out one morning, they appeared to be male which would indicate it's a type B. Close to it there's another, much younger tree (I don't know if it's Mexican because its leaves didn't smell like licorice) which actually had two fruits last year, but I haven't confirmed its type.
So maybe your friend simply has a type B and that's why he's not getting any fruit.