No, but belief in a supreme being is a Christian principle. Not exclusively or uniquely Christian, but part of the Christian package.
I don't see how it serves the argument to dodge this.
Technically and Trivially true, but so what?
If the argument is that
some of the principles the country was founding on are the same as
some of the principles of
some versions of Christianity ... yeh, that's probably true, but again, so what? I'm pretty sure that's not the intent of most people that feel the need to say the country was founded on Christian principles.
You can also say that some of the founding principles are the same as some Muslim principles
And some Jewish Principles,
and some Hindi principles,
and some Buddhist principles,
and some Wicca principles,
and some of Charles Manson's principles,
and some Jedi principles,
etc.
That's all fine and well until you try to use it as a reason to give special consideration to one religious view over others, or none. (which in my experience is the only reason anyone brings up the founded on Christian principles crap.)