If it was just a single slit running in the same direction as the rim then it still could be a pinch flat... maybe. Or it could just be that the tube was caught between the tire bead and the bead seat of the rim. Sometimes they blow when you inflate the tire, but sometimes they wait for you to be in the worst possible place and maybe even several rides after installation.

If you are running low pressures, you might consider pumping them up to max after installation then reducing pressure to what you prefer to ride. That'll maybe let you experience the results of a bad installation sooner when still at home instead of later.

Your valve stems always stand straight from the rim don't they. If they lean then that's a problem. Also usually a sign of riding with too low a pressure.