Yes it is using the same SDA and SCL lines as the Si5351 just a different address. The display is a 5v one. I didn't know there was a choice. I separated the Nano and display so I could mount the Nano with the USB port at the rear of the case and use a 20x4 display. I wanted to add an S meter and maybe a output/swr meter so I wanted the additional lines. It made more sense to run only 4 wires to the front panel and it was pretty easy to change the sketch to accommodate the new display, only three or four lines to change.
Your other post about birdies I have not done a side by side comparison but I use the Bitx a lot for digital so I have tuned around on USB and it sure seems to have less birdies and what is there seem to be at a much lower level. ?
Jeff