Something was probably eating the buds before the flowers opened, so that damaged the petals. Hard to know what it is, but here in Florida we have thrips that tend to be the bane of Vanda growers.
Like FSUOrchids said, in Florida, that kind of damage is caused by Thrips. Down here there's a simple cure. I use either Ortho Rose & Flower or Bayer Rose & Flower. Those products are both intended for use on buds and flowers. When vanda spikes are just 3"-4" long I spray the spike from about a foot away so I get a fine mist. I spray from two directions. I repeat that process once a week for 3-4 weeks. Don't spray when the buds are maturing and you see a little color change in the bud. The spray can leave spots on the flower at that point. This process works like magic for me and it often just takes three applications. Apparently that's enough to keep the thrips from getting established enough to cause damage. Good luck.