Even today the Latin word tabula is sometimes used in English, for example in the phrase "tabula rasa" (an erased slate - or an empty table :-D); in Latin, it meant a slate or a wax tablet, the two common things on which one could write or draw and also erase or alter what was already there. And that's where English got the word table from.

So one meaning of "table" is something that can record information and whose contents can be deleted or altered. One special meaning was for such a thing where the information was organised into rows and columns. This special meaning antedated relational databases by a very long time, and given what the storage structure in relational databases is it's not surprising that people noticed that the storage structure consisted of something for which we already had the name "table" and didn't bother to invent a new name.