You've got to read it carefully. Yes, you can get
free dining when you purchase a 6 night, 7 day vacation package. But you can also get it if you purchase a 3-night vaction package, an 8-night vacation package or a 12-night vaction package. There's nothing in the ad that says you are REQUIRED to purchase a 6 night package. They also don't bother to spell out that you only need a minimum of 2-day tickets.
The only "rules" to remember for free dining are:
1) The reservation must be a package. Room-only and DVC points reservations are not eligible.
2) The room price will be assessed at full rack rate (what they are really doing is discounting your resort package the amount of the eligible dining plan. Free dining is a resort discount, not a restaurant discount. The restaurants have no idea if you have a free dining plan or a paid dining plan; to them, there is no difference.)
3) You must purchase at least 2 day base tickets for each person on the package age 3 and older (you do NOT have to purchase length of stay tickets, but you do have to get the same type and length of ticket for each person registered age 3 or over)
4) Reservation must be 3 nights minimum, 14 nights maximum (21 nights for UK)
5) No other discount applies as WDW does not allow stacking of discounts.
6) "Ticketless" packages with dining (for annual passholders or military) are not eligible for free dining. Everyone who wants free dining must purchase the minimum 2 day park tickets as part of their package reservation.
7) You must check in to your resort during the promotion dates to be eligible for free dining for any part of your stay.