Is this dimmer wired the wrong way around?
I do believe it is wired backwards.  That would never be tolerable in a DC (direct-current) system.

However, AC reverses 100 times a second (giving 50 full cycles per second). A funny side-effect of that is that some things don't care about being back-fed, e.g. breakers. 

If your dimmers are one of those, then you got lucky. 

However, I would expect that such a direction-agnostic dimmer is not very LED friendly.  It's really past time to upgrade to LED lighting. They have been quite good for several years now. The power bill alone will pay for the dimmers inside a year.