Just a wild guess, but the recall notice that was mailed to owners advised not having a passenger sit in the front seat until the recall work (replacement of the airbag) was completed. There were owners that complained that this forced them to choose between using the car in a potentially dangerous state and not being able to take trips with more than 2 or 3 passengers (all in the back). The stock of replacement airbags was low and wait times for parts were long. It's possible the previous owner had the dealer disconnect the airbag while waiting for parts to arrive or just did it themselves.
This is something you can see with the glove box removed- the connection is a bright yellow wire.
CAUTION: if it is disconnected, do not re-connect it yourself as this could cause the airbag to accidentally deploy.
You can check whether the recall was issued for your Vibe here:
https://my.gm.com/recalls
Unfortunately, not all the recall work was done properly and there were reports of Airbag lights coming on afterwards. One of the drawbacks of having a re-badged Toyota being serviced at a GM dealer that sees few Pontiac Vibes...