x86 is actually 32bit programs.
The OS is presumably 64bit, Samba is 32bit fo goes in that programs folder.
In 32bit windows there is just the programs folder as 64bit os can run 32bit software buy 32bit od cannot run 64 bit software.
Sure someone else will know why but I never got round to looking up why 64bit is x64 but 32 is x86.
32 bit applications are installed in Program Files (x86) but native 64-bit applications run in the “normal” Program Files folder. The x86 version is there for backwards compatibility so that you can run 32bit applications on a 64bit OS. So you need both folders.