I think Tekka’s ribbing about Ren’s family pissed him off, so he killed Tekka in anger without really thinking about it. He probably assumed he could search the village and find some clues, then Poe appeared and he figured Tekka gave Poe the map and thought “Oh, cool, I didn’t fuck up that bad” and took Poe to interrogate him.
That’s my 2¢, anyway.