It’s fairly common with calls over a cellular network from or to any cell phone. It’s usually a quirk of the network, especially if disconnecting and calling back fixes it. It means that the first connection was with a more distant tower on one end of the call or the other, and is especially common if you or the other phone are moving around at the time the call is received. The phone will stay connected to a tower as long as it can, but when you call back the network will switch to the nearest tower. Do you notice a change in signal strength (“bars”) between the initial poor call quality and the call back?