You cannot say a software is only #OpenSource but not #FreeSoftware in practically almost all cases.
Software that qualifies as Open Source but not Free Software is possible, but such licenses are used only by a tiny negligible number of software.
So what is the difference? The choice of term reflects your motivations and priorities.
So if you care about Free Software philosophy, just ask people to use the term Free Software.
Don't call any Software or license as Open Source only.