"Ground" as a verb has several meanings.
One is what you are thinking of, to "restrict". This meaning comes from aeronautics. If an airplane or a pilot is unfit to fly, we say that he or it is "grounded", that is, not allowed to leave the ground. From there the word has come to be used whenever someone is restricted to some "home base". Like parents may tell a teenager that he is "grounded", meaning he is not allowed to leave the house. Or a boss may tell an employee that he is "grounded", meaning not allowed to pursue some project that he wanted to.
But that's not the meaning here.
The relevant definition of "grounded" is "provide a basis for" or "supplied with basics". For example, we might say, "Bob is well-grounded in basic physics", meaning that he know basic physics very well and can apply this to more complex subjects. Or, "Smith's political theories are grounded in the works of Hume and Friedman", meaning that these works are the basis for his theories.
In this case, the writer is saying that celebrations should be based on the recognition of certain facts. You shouldn't base your celebrations on other ideas or theories, but on the ideas that the writer presents here.