Final answer:
The given information does not provide details about the number of people who greeted Titanic survivors on April 18.
Step-by-step explanation:
Based on the given information, there is no direct reference to the number of people who greeted Titanic survivors when they arrived on April 18. The provided information mentions events related to the Titanic, the St. Louis, and the Lusitania, but does not provide specific details about the number of people greeting Titanic survivors on April 18. To determine this information, additional sources that specifically discuss the April 18 arrival of Titanic survivors would need to be consulted.