There is no right answer. It depends on the receiver, the quarterback and cornerback's positioning.
The quarterback being better at short or long passes affects the decision.
If the receiver is fast but not shifty then a short pass may invite more risk than reward as the corner is going to be coming at him full bore once the catch is made. Thus, the long pass is the preferred route. However, if the receiver is difficult to tackle then a short pass can easily turn into a long gainer. So if the corner plays back then a short pass is the way to go. If the receiver is tall then the long pass may be the best play regardless of situation.
However, the over-riding factor is that it depends on where the cornerback is playing. Generally, if the cornerback knows the receiver is faster and they aren't going to get safety help then they aren't going to put themselves in a position to get beat deep. So they'll play loose and a short pass will guarantee a 5 to 10 yard gain with almost no risk. If they play bump and run then the quarterback hopes the receiver gets off the line and they'll be looking long. However, with no safety help, that means a blitz is coming and if the receiver doesn't get off the line cleanly then there better be an alternative receiver or the quarterback is going down or risking an interception.
So bottom line, you are both correct and you are both wrong.