What does it mean to be ostensible? (From Twain's A Connecticut Yankee in King Arthur's Court)

Ostensible means plausible rather than demonstrably true or real; apparent.
These poor ostensible freemen who were sharing their breakfast and their talk with me, were as full of humble reverence for their king and Church and nobility as their worst enemy could desire. There was something pitifully ludicrous about it.

From Mark Twain's A Connecticut Yankee in King Arthur's Court.