Could not power it off. Managed to start up Download mode again. Did a TWRP reflash then.
Then I forgot to uncheck auto-reboot, but what happened was that it restarted into the frozen teamwin screen again.
Now did it again - reflash of TWRP. Auto-reboot unchecked, reboot according to the instructions in that guide above (vol down+home+power, when screen goes dark immediately go from vol down to vol up). Back at the frozen teamwin screen again…