This isn't a western raffle, it's a Japanese kuji pulling. You can buy these things one at a time and know if you've won immediately. They're saying the expected value of pulling one ticket is .8 given that 1/5 tickets in the thing are winners. If you pull a ticket and know the result, then depending on the numbers of tickets, you can recalculate the odds, but when you pull the first one, it's 1/5. They're probably using that example instead of rolling a die or flipping a coin because drawing kuji is more familiar to a Japanese audience.
But yes, assuming there are more than 5 tickets in the thing, you're not guaranteed to win once every 5 pulls. (Unless you pull all the tickets out.)