It could be, or it could be just that it is at the end of it's bloom cycle. When you buy an orchid "in bloom", you don't know how long it has been in bloom, and some can stay in bloom for months, while some blooms last only a day. I have Phals that the blooms will last for months, and Sobralias that only last 2 days, but will put out more blooms as the old ones die. Some will drop buds with a sudden change in atmosphere.
I don't do well with Oncidiums, so I can't tell you for sure.
