Alternatively you can also claim it in one click from Steam.Alternatively you can get from Humble Bundle.
Buy Oddworld: Abe's Oddysee® from the Humble Store
Nope, those are discounts offered by third party retailers - in this case GMG (-15%). In Steam US, it is still $100 officially. So definitely a price glitch which will be rectified soon, probably today as it is the first day of release so high chances of glitch getting noticed.