The average is the sum of the proportions in the bootstrapping sample divided by the number of resamples.
Minitab displays two different proportion values, the proportion of the observed sample and the proportion of the bootstrap distribution (Average). Both these values are an estimate of the population proportion and will usually be similar. If there is a large difference between these two values, you should increase the sample size of your original sample.
Because the proportion is based on sample data and not on the entire population, it is unlikely that the sample proportion equals the population proportion. To better estimate the population proportion, use the confidence interval.