what made jimi hendrix flip his guitar upside down and play with his left hand?

I think Beatnik has a good answer. Here is a little more information on this:

James Marshall Hendrix (born Johnny Allen Hendrix; November 27, 1942 – September 18, 1970) Hendrix was born on November 27, 1942, in Seattle, Washington, USA, while his father was stationed at an Army base in Oklahoma. He was named Johnny Allen Hendrix at birth by his mother, 17-year-old Lucille Hendrix née Jeter.[16] She had put him in the temporary care of friends in California (a holiday). On his release from the Army his father, James Allen “Al” Hendrix (1919–2002), took him, and changed his name to James Marshall Hendrix in memory of his deceased brother, Leon Marshall Hendrix.[17][18] He was known as “Buster” to friends and family, from birth.

According to fellow Seattle bandmates, he learned most of his acrobatic stage moves, a major part of the blues/R&B tradition, including playing with his teeth and behind his back, from a fellow young musician, Raleigh “Butch” Snipes, guitarist with local band The Sharps. Hendrix himself performed Chuck Berry’s trademark “duck walk” on occasion.[25]

His flashy style and left-handed playing of a right-handed guitar already made him a standout.

Hope this helps

Candy

Unauthorized Biography of JIMI HENDRIX (5th of 12)