The Putoline 959 is a 2-stroke oil.

Probably they do that as in the same way I had my 1st thoughts. Any methanol friendly (mixable) oil will give less mess inside the engine and giving a good start and lubrication.
Standard motor oils which do not mix with methanol can a give strange gray blub inside but when most oil has dripped out I have not seen an issue. And if you clean it all out with brake cleaner and re-oil it all with afterrun oil for sure nothing can go wrong.
Be aware that most castor oils have a high viscocity and do not provide the right lubrication for this way of breaking in an engine.

I was also thinking of Marvel mystery oil. It even has a lower viscocity and is a well known used afterrrun oil but never tryed it.