Even if you tighten it like a sissy, the coolant wouldn't pour out like that. I have seen even more experienced mechanics than me, make the same error numerous time. Having said that, they kinda knew what was at fault when the coolant poured down the block

On the other hand, some gasket patterns are quite alike whether you turn it upside down or not, but it's not quite there, whick would manifest itself as a leak preeeeety soon. Remove the intake manifold and double check, im sure that's where the fault lies.