Buzz-Buzz is From the Present
I believe Buzz-Buzz wasn't a traveler from the future, but a being from today. Think about it, he had PSI, so in all possibility he could have had a premonition about what could have happened in the future. Then, he could have used his powers to travel to the future and try and alter it.
However, he couldn't beat Giygas. Then he heard of the legend of the Choosen One, realizing that he (the Choosen One) lived in his (Buzz-Buzz) time, Buzz-Buzz went back in time to get the Choosen One. However, he had to phase-shift to travel back in time, (just as Ness and Co. had to do) thus explaining the bee shape.
But, another possibility is that it is really Ness who went back to warn his past self of Giygas' plot. However, to avoid a paradox in time, (watch the "Back to the Future" trilogy to find out more) Ness transformed into Buzz-Buzz. This would also explain Buzz-Buzz's grave in Magicent (due to the fact he too was Ness).
If you disagree with me then e-mail me at: [email protected].