Sparrow Ultimate

Hello Apex family. I have a question about sparrow's ultimate. I was playing Watson, and I had a gen in the corner of the building. The enemy sparrow threw his ultimate and instead of my gen eating the ult, the ult destroyed my gen and all the fences inside the building. I expected it to destroy the fences but not the gen. Can anyone advise if the sparrow ult overpowers the gen or maybe the gen was weak? I would love to know.