This is a very good question. It can be argued that risk parity is one example of a smart beta strategy.
Yet it is important to understand that both are coming from two different directions: risk parity is basically a form of risk management (in the sense of risk-adjustment) because its basic approach lies in diversification - like the alternative methods mean-variance optimization, 1/N, minimum variance and so on. Comparing it with mean-variance it is also an answer to the estimation problem because variances are more robust than covariances and you don't have to estimate means at all (which are notoriously hard to estimate).
Smart beta strategies are more coming from an income generation perspective: You try to find the factors that contribute most and overweight them. In this case one does refer to the low volatility factor (or anomaly depending on your school of thought).
So in this case both perspectives meet because you see something that results in a risk reduction also as an income generation vehicle and at the end the resulting portfolios could very well be the same, so as I said in the beginning risk parity can be seen as one example of a smart beta strategy.