tbh you're basing this on pedantry
they used the word "embargo," sure, but using that as a basis for recognition is just being really technical
it's very clear what they meant
well they already used blockade to refer to actively restricting the flow of goods to and from a specific location/nation
by saying embargo, they've effectively ceased trade relations between them and another entity, in this case, the confederate states
they're two different words and they have two different definitions for a reason