No, TalGelman- is correct. The placement of the adjective alters its meaning. Before the noun, gran means more of an abstract bigness, which in English we translate as greatness.
Here are some other words which make a similar distinction:
hombre pobre = physically poor man (pauper)
pobre hombre = poor (unfortunate) man
amigo viejo = physically old (elderly) friend
viejo amigo = old (longtime) friend
Mira ! for example: Tu tienes un gran corazon = Tu tienes un corazon grande. Here has the same meaning. I understand what you are seeing, but it is not the case here.
I think that here the right translation is "It was a moment of big confusion" , because "great" is a positive thing AND "a confusion" can be like a small mistake. So, i think that is not correct to say "great mistake" or "great confusion" , the correct would be "big mistake" or "big confusion"
Ah, creo que veo la turbación. In English, great doesn't just mean very good; it also means large in scale or scope. Nobody thinks that a "great disaster" is a positive thing.
We do say "big mistake", but not "big confusion". I believe it's because confusion is not a countable noun: you can't have two confusions; it doesn't make sense.
And just like in Spanish, a big heart (un corazón grande) is a metaphor. It doesn't mean that the heart itself is literally bigger — that would be an enlarged heart (hipertrofia del corazón). Metaphors by their very nature break the rules, and therefore aren't the best examples of how grammar should behave.
Confusion is a non-count noun. There needs to be an adjective between 'gran' & confusion for it to be correct grammatically. Fue un momento de gran cuantidad de confusion. A positive adj. before a negative noun do not work well in everyday English except in jokes, sarcasm etc.
If a translation seems easy, like for confusión, I always hover above the word (sometimes before I type my answer) to see if there are any 'unexpected' translations. In this case, I saw "embarrassment", which actually seemed quite fitting, so I typed: It was a moment of great embarrassment. Not accepted. So... is it incorrect?