It never ceases to amaze and perplex me that people who should know better say such utterly absurd things about non-Christians worshiping and believing in the one, true God. I came across this wonderful comment by Dr. Martin Luther, who said:

He who wants to know God, love God, worship God, and serve God should learn to know Christ aright, should love Christ, should worship Christ, and serve Him. To know, love, worship, or serve God without Christ is impossible.

Source: What Luther Says (CPH: 1959), Quote 476, p. 160; Weimar 52:732)