American law absolutely applies globally when it is applied to American citizens. People who don't realize this routinely end up in jail.
Stuff like the drinking age (a state law) doesn't apply, but federal laws do apply, which is why American citizens who go abroad to commit gang-related crimes (and more stupidly, break fishing and hunting restrictions) are still arrested when they return despite the fact that no aspect of the crime touched American soil.
Please don’t misunderstand. Most countries (all that I am aware of) apply their laws to all people within their territory and to their citizens globally. The Indian Law in question applies to non-Indian citizens outside India. That is a big difference.
Facebook is an American company with a lot of American employees. It also has a lot of Indian employees, and I assume those will be held responsible if things don't go well.
Stuff like the drinking age (a state law) doesn't apply, but federal laws do apply, which is why American citizens who go abroad to commit gang-related crimes (and more stupidly, break fishing and hunting restrictions) are still arrested when they return despite the fact that no aspect of the crime touched American soil.