Magic Tricks

Simply, it's called marketing.
In your example, purposely avoiding specific pricing, I'll explain the basic concept.
If a vendor makes a mistake (or not) and the customer benefits, as in your example, then it cannot, by definition, be misleading. They are honoring their 'mistake'. Thus, there is no detriment to the client/customer. Simply, no harm, no foul!
Psst...I assure you...it's not an error ;-)
If a vendor stated a price was good until a specified time and then altered/decreased the time period of that 'bargain' i.e. shortened the 'sale' time, without a reasonable explanation/cause, then that could be an issue.
Regardless, if you like the course, then get it at a great price.
There are some great sources of info in this package.
Best wishes...

Uh oh - MYoda is spewing that law school stuff.
That 'reasonableness' standard always gives people away.
Just kiddin'