They are not the same. That is, they use the same engine, the XeTeX engine, but they are for different formats. The XeTeX option is for use when writing plain TeX, while the XeLaTeX option is for LaTeX.
The document lualatex-doc describes the difference between an engine and a format. I quote:
To answer this question, we need to mention a few details about the
TEX world that you may usually ignore: the difference between an
engine and a format. An engine is an actual computer program, while a
format is a set of macros executed by an engine, usually preloaded
when the engine is invoked with a particular name.
Actually, a format
is more or less like a document class or a package, except it is
associated with a particular command name. Imagine there is a command
latex-article that would do the same as latex, except you wouldn’t
need to say \documentclass{article} at the beginning of your file.
Similarly, in current distributions, the command pdflatex is the same
as the command pdftex except that you don’t need to put the
instructions to load LaTeX at the beginning of your source file. This
is convenient, and slightly more efficient too.
Formats are great
because they implement powerful commands using the basic tools an
engine provides. However the power of the format is sometimes limited
by the engine’s tools set, so people started developing more powerful
engines so that other people can implement even more powerful formats
(or packages). The most famous engines now (except the original TEX)
are pdfTeX, XeTeX and LuaTeX.
