You say you moved the plants out in May, and by April she was budding. That makes no sense. April is before May, bro.

Anyway, to answer your question nonetheless, if you take a mature plant grown under 18+ hourse of light indoors and move it outside in March-May, then the plant will start to flower becaues the sunlight at that time mimics the Fall. This is a good way to avoid the prying eyes of the law, who look for mature plants in the Fall since that is when outdoor grows naturally flower.

see INDOORS & OUTDOORS - CONSTANT HARVEST STRATEGY, light, flowering, harvest, marijuana plants, cannabis plants