Kitchen reno

Two days ago we had the kitchen gutted. We shut off the water under the sink, of course, and now just have the sink waste pipe sticking out of the wall. We noticed that when we flush the upstairs toilets, that there's a loud gurgling in the kitchen waste pipe and some water comes trickling out. It happens only when we flush the upstairs toilets, never when just running water in the upstairs sinks. Do we need a plumber???

yes , you have a partial blockage