This is a common issue with this strain especially. I received one the same way. Apparently it's not that the pack popped, there's something to this strain and CO2 buildup when shipped under temps where the yeast warms. Wyeast says:
"25. What are the causes of swollen packages? Can you sell them?
Swollen packages are almost always the cause of a small amount of sugar or CO2 being left in solution at the time of packaging. Upon shipment, CO2 can be released from solution or the yeast can consume the sugar and create a small amount of CO2. Cell autolysis, or cell death can also be a cause of swelling packaged. However, this is only in rare cases where the yeast is exposed to high temperature for an extended amount of time. If a package is swollen and has not been mishandled, it can be sold with confidence."
There's also one Homebrew online store that has a note about this strain and says it's common that they come inflated and that it's normal and they will not refund or exchange for it... I just can't remember which store it was.
Anyhow, don't worry about it, just use it.
Rev.