If only one person made the comment the pace was too fast, I would chalk it up to a unique reader response. When I get three or more comments of the same criticism from different readers, I then know the flaw is in the writing.
Pacing can mean several things, in terms of what a beta reader might really be reacting to. Many times, this criticism really means a scene has been passed over and needs to be developed more. These are scenes with a major conflict or revelation which can be exploited for more effect, but the writer left this potential untapped by telling instead of showing.
Also, somtimes slowing down the pace will build tension, instead of relaxing it. Whenever Hitchcock wanted to amplify tension, he would do it by detailing every little event in a scene, while suspending the danger to the main character.
So even though the films would slow down in these scenes (Spoiler: think of how long Cary Grant waited by the road for his secret meeting in North by Northwest, before being attacked by the plane... the pace was exceedingly slow)... the tension was never higher.