Husky one,
Thank you for stressing the concept, you are perfectly correct,
so 500m... taking into account that in these situations RVR is seldom stable maybe they got a value higer than the minumum at the time.
This could be the case because as reported on
www.flightglobal.com,
the next incoming a/c, a Wizzair A320, had to wait for the runway
to be clean from debris and then made an uneventfull landing; probably
with ALS out and in this case the RVR goes up to 1000m. But probably they
busted the minimum as well.... no