Definitely looks like sunburn. It also looks thirsty judging by the wrinkled look on the leaves. That is one amazing specimen!!! I would pay a fortune for that! I wouldnt worry about repotting it since it would disturb the plant and delay flowering, and cattleyas look incredible when they flower on a huge plant. Try finding a wood slat basket big enough to put the whole thing in, and give its roots lots of mistings. I am super jealous!! That is such a great plant!!