One man pulls the trolley. Another stands on the trolley, pulling a lever back and forth. The lever operates a pump that sends water from a tank (on the trolley) along a hosepipe to a third man, who is holding its end and spraying the flowers.
In India, there is no shortage of manpower and wages are not high. So, employing three men to do what a costly sprinkler system would do in Western Europe makes sense and gives employment to those who have families to feed.