from what I see the downloaded compiled source and hence binary is in one directory and the source code to run may be in another.
if they added a softlink into the bin directory, they could forego having to always include the path in the calling the binary.
ln -s /lua-5.2.3/src/lua /usr/bin/lua
chmod 755 /usr/bin/lua
then from the source directory lua hello.lua should work