Apparently, under the sheets a PIPELINED function will create SQL types and collection types.
If you run...
and then check USER_TYPES, you'll find that it creates three types prefixed by SYS_PLSQL_, followed by a number (which looks like it corresponds to the OBJECT_ID visible in USER_OBJECTS) and the rest of the identifier.
CREATE OR REPLACE PACKAGE PFP_CONSTANTS_PKG IS
TYPE v_rec IS RECORD
TYPE v_array IS TABLE OF v_rec;
function dummy return v_array pipelined;
So if you find some types with that sort of prefix, you'll be able to track back to the package which created them.