I wonder if those tourists were flouting the rule or unaware and just being made an example.
The article says they were German, so it is very unlikely they deliberately flouted the rules; Germans just don't do that. German pedestrians crossing a road will wait for the green man even if its clear for half a mile in both directions.
This will be Venice getting uppity. They are sick to death of all the tourists, there are plans to tax every tourist from next year. 600 giant cruise ships every year park up in the main canal, disgorging thousands upon thousands of tourists into the narrow streets. They wander about, slowly, blocking the footpaths, taking photos, perhaps buying cheap tacky souvenirs. They won't take a table at a restaurant because they have free food on the ship. They won't go shopping because they have shopping malls on board the ship. Some of the tourists don't even realise it is a real city, with real people trying to lead their own lives. One tourist guide was once asked "What time does it close?" as if it was Disneyworld.
Welcome to Britain, if you don't like the weather, just wait a minute, some more will be along soon.