IHG Rewards Club had their Cyber Week Sale that run from the Black Friday through Cyber Monday and offered various deals from discounted rates to bonus points for signing up for Ambassador membership (read more here).
You an access IHG’s page for this now expired sale here.
Seems that the person who programmed this offer at the IHG’s end must be either math challenged or encountered fat finger incident. The bonus points are posting at 500% instead of 50% bonus.
Wouldn’t surprise me if IHG fixes this posting issue retroactively and claws back the unexpectedly generous bonuses back from the accounts they were posted.
If you decided to use them now, expect that your account will go into negative territory (unless you have enough points in your account).