Well, that opinion has some merit but there are a whole lot of other things to consider. 13 innings is a really small sample size to draw too much from. Typically, in HS, you would want to give your opponent a different look with a reliever. But so many variables. Maybe lefty #1 was very effective but hit a pitch count. Maybe opponent has a bunch of LH hitters. Maybe the two lefty pitchers have different styles, pitch types and velos. Maybe the opponent runs well and a LHP can help shut that down. Maybe some opponents flat out rake and some don't. Maybe coach is limited by who his best options are and what the move will do to the rest of the lineup and defense.... just for starters.
Yes, all things being equal, I'd prefer a righty after a lefty. All things are never equal. Heck, I'd also prefer that righty reliever throws 92 with pinpoint control and nasty stuff too. Oh, wait, I don't have that. In fact, after I rule out my starters, I save my fourth best pitcher to close and my fifth best is a lefty who throws seventy somethin' but has decent control. Sometimes he gets outs. Sometimes he gets racked.
If the kid is a good P, he will get the job done more often than not. Period.