This is a result of a number of factors more than likely. Root cause is a bad detergent/soap to water ratio, which can be caused by putting too much in or unexpectedly soft water (people who are used to putting hard-water amounts of soap into washing machine loads who suddenly move somewhere with super soft water will often do this once or twice before dialing it back), but a contributing factor here is likely that the drain line that the hose is dumping into is partially clogged, so the suds are having a chance to backflow up past the hose instead of staying with the flow of the water, or the wrong type of soap is used as was mentioned above.