Depends on which null hypothesis you're testing. He told us that he rarely had a down day, and based on Bitcoin's volatility I'd say it's reasonable to assume the probability of it going up or down on any given day is a coin toss (regardless of the longer-term trend and independent of other days). Thus the probability that he's a day-trading monkey is 0.5^n, where n is the number of up days he had in a row. (since he had a few down days it's actually a binomial coefficient but the value is < 1e-80 anyway, far less than a conventional p-value of 0.05)

On the other hand, if we wanted to test his 3900% yearly return, we might assume that monkey returns are equal in distribution to Bitcoin's price and then test the hypothesis that he's a monkey via something like a paired t-test. The problem here is that we only have one data point so p-value is undefined, and due to high variance it would probably take about n=10 points to get something significant. The upside of this approach is that you can get a confidence interval for how much better he is than a monkey, instead of just a yes/no answer.

In any case, since the author has at least 365 data points, he probably has an extremely good idea of both a) whether he's a monkey, and b) how much better he is than a monkey.