That is how they are defined in set theory based math. The mathematical definition is not the only meaning of a word. When when start to talk about the physical world, we need additional concepts. You are welcome to read the wikipedia page about correspondence theories of truth.
The fact is you are talking about the meaning of words. Be they English words; or Mathematical words.
If you are going to talk about the correspondence theory in the same breath as you are talking about any language - you need to solve the symbol-grounding problem.
What function/mechanism/relation (or if you don't like any of those words - pick your own) grounds symbols?
That is how they are defined in set theory based math. The mathematical definition is not the only meaning of a word. When when start to talk about the physical world, we need additional concepts. You are welcome to read the wikipedia page about correspondence theories of truth.