Given that you're posting a line graph rather than a candlestick chart, and given what you said in the OP, I have to wonder if you understand what arbitrage trading is, what spreads are, etc.

Do you think that there is, at any given point in time, one single BTCUSD exchange rate?

There's not. It's like the planets of the solar system moving together with the sun. Market participation occurs at different exchanges and not all market participation is evenly distributed so some exchanges will get slightly more or less action than others at any given point in time. This makes each exchanges orderbook unique and when prices top out or bottom out, the raw numbers are going to be close but slightly different.