1. He may have been shooting HDR
2. Or been bracketing
3. Testing a new camera
4. Hoping for the stag to stick its tongue out
5. Learning the difference between single and burst shooting
6. Seeing if the noise would startle the stag in those conditions
7. Demonstrating different methods for teaching purposes
8. Playing devil's advocate because he suspected there may be a single-shot-only-straight-out-of-the-camera-editing-is-for-losers purist in the vicinity and he wanted a giggle
9. Camera was jammed on burst
10. Because he knew for an incontrovertible fact that there is no 'right' way to take a photo, and this was his preferred, practised, and proven technique, it worked well for him, and was no-one else's bloody business.