In an engineering discipline, asserting that someone is 'flying blind' could very, very easily be taken as offensive. Knowing what's going on and why is so fundamental to 'good engineering' practice that you basically are calling the people ethical failures. 'Impugn' is a perfectly reasonable word for how someone might react to such an aspersion.

Maybe in the future don't accuse engineers of 'flying blind' if you aren't inviting return fire.

From context there was a lot of conjecture going on, but the big challenge with building something new is what order to build the bits in to give you the most useful information fastest. As the number of people goes above 2 the odds that everyone agrees or that 'everyone' is right drop rapidly toward zero. You do the best you can, and hope it's good enough that you still have time to react to the worst of the decisions you made earlier. But it's not 'flying blind'.