wa alaikum salam
the term you said "Assalamo Alaikum (wa rahmatullah)" literally means "Peace (and God's blessings) be upon you"
So, we can take that as you are theist.. Someone believing in an absolute being, Ik Onkar, Jehovah, God, Allah (though the attributes people think of Him may change but still one God..) and I think there can be mu'min/believers in every religion (ie. 2:62), knowing that there are levels of belief (4:136). However, for the concept of being Muslim, as Murtaza Mutahhari says, so, as brother loveroftruth says, you need to ask yourself if you believe in an absolute deity (God) and the hereafter.. and if you have love in your heart for the seal of Prophets.. if you do, you are a muslim inshaAllah..