Well flagging is usually a quite poor reaction, even as a retaliation as at worst. This means I see his flags also as a poor reaction to whatever issue you have with each other. It seems he momentarily muted you and flagged two of your comments you had left to him?

The advise here and in above are also for @weirdrat. If you just have issues with each other, the best reaction usually is to leave the other one to be. You've been here longer @stehaller and I'm assuming you too know there are rarely winners in flag wars, as at worst it might escalate :)

Good luck you too, I will not interfere any longer!