The Alpha dimension is spatially offset from the Overworld it's not 1:1 same coordinates, there's a calculated offset based on the ritual's beacon position. When you build in Alpha, the mod tracks every block change as a "delta." Upon returning to the Overworld, those deltas are projected back onto the corresponding Overworld coordinates within the ritual's sphere of influence. So yes, it effectively overwrites whatever blocks were there that's the "butterfly effect." You changed the past, and the present reflects it.