How does TubeBuddy calculate the average of the last 5 videos? Over what time frame are these values calculated? How often does the keyword explorer update its values?
It's the median views of the last 5 videos that are at least 3 days old. It's updated every 2 weeks.
YouTube's analytics data has a 2-3 day lag before it's available, which is why there is a 3 day threshold.