Yesterday's CRYPTO charts BTC and ETH - identical?!? Why

I have noticed (and as I read others too) that the two mayor CRYPTO's BTC and ETH have had the almost identical price action. I have a little suspicious over that matter due to two separate markets that should be at least a little bit different.

I have a picture (sorry because I have not taken a little bit more time and scaled correctly but never the less - you can see that the pricea-ction was almost IDENTICAL. Coincidence? Maybe - but I do not like them...

Any ideas why ? I would like to know explanation.