It is of course unknown who the first philosopher was (and Cain would be a strong contender for those who believe in Creation). But the first philosophers we know under the title are Greek.

This could have to do with documentation. Writing was a rather obscure science in the Ancient Worlds. And script developed slow from strong symbolism to the more abstract and versatile tool we use today.

The Greek had a script like ours in which nearly everything what can be spoken can be written (as opposed to the Egyptian Hieroglyphs, or even the Chinese Kanji, even though Chinese Philosphy developed but in another way.).

Then the Greek had not the same monolithic political system other countries had with a strong emphasis on a Pharao or great King). This could also have contributed to the development of more abstract problems than watering.

But all in all I do think that the Greek were not the first philosophers. But we don't know too much about the philosophical ponderings of the others.