You can use the ClassAliasMapper in Xstream to give the items in your collection a different tag when serializing to XML.
You add a block like this (for each collection: stats, count, test):
ClassAliasingMapper statsMapper = new ClassAliasingMapper(xstream.getMapper());
mapper.addClassAlias("somethingAnother", String.class);
xstream.registerLocalConverter(
InteractionSession.class,
"stats",
new CollectionConverter(mapper)
);