I think about 300% of Luffy is in the water at this point, eve Robin does as well.
LOL, that's still his Limb filled with Air. Robin is only using Limbs as well.
Well the best I can come up with is that it's a PIS moment. When Jinbei Shoots Luffy with a Log to the Admirals in a Stream.
Or we can come up with excuses.
So lets try coming up with excuses.
A. We can say that Luffy's will overcame his weakness.
B. We can say Holding a Log while submerged in Water for Devil fruit user is possible and isn't that hard. Even though Oda describes in the SBS as almost impossible.
C. We can say the "Sea" Oda describes in the SBS like rivers, pools, and baths etc all literary have to be standing water. So any moving water like Streams or geysers don't count. So Knock up Stream should not effect Devil fruit users.... LOL
D. I don't know I think its just PIS....