Question

What does it mean to say that Gothic architecture was disseminated

Answer 1

Gothic architecture was pointed arches, ogival or ribbed vaulting, and the flying buttress.
When we say that something was disseminated, by that we basically mean that something was spread very widely. By that logic, when we say that Gothic architecture was disseminated, we're referring to the fact that the spread of culture. To say that Gothic architecture disseminated means that it spread to other countries as well outside of France, including Britain, Iberia, and Germany. 

Answer 2

When we say that something was disseminated, by that we basically mean that something was spread very widely. By that logic, when we say that Gothic architecture was disseminated, we're refering to the fact that it spread widely.