Does the theme's memory requirement exceed its given description?

A few months ago I installed the newspaper X theme in my website and according to the description given in it, the theme only needs 50 MB of RAM and it does not exceed 250 MB even if all other supporting plugins are included. But after installing it the memory exhausted error started coming in the normal VPS hosting and I had to upgrade my server. I want to know if the theme requires more memory than the given description? And what is the effect of a theme in server memory and what are its factors?