meshes in blender vs. in unity I'm trying to understand how the meshes are working in blender vs. unity.

My goal is to take an object with many meshes, and after applying the textures and the materials in blender, merge the meshes into one mesh using "join". Now, there's only one mesh for the object and I export a .fbx file.

In Unity however, after importing the .fbx file, the object has multiple meshes regardless the fact that in blender it had only one mesh. 

Can anyone explain to me why unity avoid the mesh changes made in blender?
Make sure you have "Selected objects" enabled when exporting the FBX file, otherwise all objects including hidden objects and objects on another layers get exported in the same file. Besides that the only explanation for multiple meshes per 1 exported mesh is exceeding Unity's 64,000 vertices per mesh limit that causes your mesh to import as multiple segments.