Existing light fixture is connected to 2 white wires, black wires are capped
It looks like a switch loop that was wired backwards. The always hot of a switch loop should be white and the switched hot should be black with a marking on the white always hot to identify it as a hot. I have seen this many times, it is easy to fix by swapping the white and black at each end and then marking the white wire with a black sharpie or black tape (any color other than green, gray or white would meet code)