Bitcoin fall may not be related to that, it has got to do nothing with the bitcoin. The ICO is completely different thing and bitcoin is different. What getting advertised is the different projects of ICO an dtheir features to attract many people around the globe considering that Facebook has reached to each and every corner of the world.
If ICO advertises has dropped significantly on the Facebook platform then Im pretty sure it should affect them as well as ETH currency. On the matter, ETH is the majorly accepted currency when we invest money into ICO projects. So major drop should be seen in the eth market and not the bitcoin market at all.