I guess we're looking at the sun's rays and not the reflected internal light fittings
Never seen anything like that myself, quite a unique opportunity.
The sun seems to have lit the underside of the clouds but the exceedingly low height of thee sun and mountains have limited it to that narrow slit of illumination.
Good job you were able to capture it, although a shame someone wasn't available to kill the rooms lights momentarily.
I bet it didn't last long.