No... definitely cultured. If there was one natural pearl in the whole strand, it would have ten lab reports to go with the auction! And the current estimate for the strand could have been just for that one pearl, LOL!
And no, I don't think those are all freshwater pearls. It isn't so unusual to find strands made of a mix of freshwater, south sea (white and golden) and Tahitian (lighter silver grays) of similar pastel tones. The colors work beautifully together!
Besides, the descriptions does not say what type of cultured pearls at all - allowing for the mix. Frankly, I have not noticed the type to matter much anyway.