It's on the high side, but if it's a one-off occurence I wouldn't worry too much. Keep a close eye on your stats and if there's anything suspicious in the future be sure to contact AdSense Support.
If five clicks gives you 50% CTR, that means only 10 impressions. Statistically meaningless so I wouldn't lose much sleep over it. Keep an eye on it in case you see a similar ratio when you look at that channel over a week or preferably more worth of data.