I just watched the video too right after it was posted. Very cool.
I went over to his source code repository and looked at his Local.py file in RasPiConnect
What I found was that he is using a feedback button and storing the state of the feedback button on the Raspberry Pi. He then uses if statements to cycle through a serial of images of graphs (rather than changing the whole page - he could do that too in the the Local.py file).
#check for validate request # validate allows RasPiConnect to verify this object is here if (validate == "YES"): outgoingXMLData += Validate.buildValidateResponse("YES") outgoingXMLData += BuildResponse.buildFooter() return outgoingXMLData
# not validate request, so execute
responseData = "pi power volts"
if (objectName is None): objectName = "pi power volts" lowername = objectName.lower()