Definitely not a standard thing.
Putting a load on first thing in the morning and hanging it out once home from work is a really normal thing to do. As is putting it on in the evening and hanging out first thing in the morning.
Feeling that a load needs to come out very soon after finished is the more unusual approach. Mould growing in door seals is a valid concern, but that won’t come from the machine staying shut for a few hours after finishing running. It happens from being left damp but door nearly shut. So you get damp and no air circulation. When the cycle finishes the door seal is engaged so there’s no damp sitting across it. You want a machine left properly shut until it’s emptied. The mould growing scenario is when the load finishes and the door gets opened and left ajar but machine not emptied. Stay away from that set up and machine is fine and washing is fine. Leaving within a same day period won’t do machine or clothes any harm at all.
(and conversely, for some types of clothes and dyes, drying in direct sunlight will fade them very very quickly so there is a good reason not to do with it those. Eco dyes are prone to it).
It sounds like you place a relatively unusual emphasis on importance of a particular approach to washing and drying clothes. You tend to find people’s views on drying indoors are very split depending on whether they’ve ever had issues with damp. Damp issues are generally a feature of the property. In some properties you can do pretty much anything and never get damp. In others, you have to be meticulous on how handle all moisture otherwise will get damp rapidly. Sounds like you’ve experienced the latter which will make you cautious.
It’s your house, you get to pick what’s important to you. But when you communicate that, do it with some context that this lodger isn’t doing anything that a lot of responsible home owners wouldn’t think is perfectly reasonable behaviour. They may be trying to be considerate and you’ve just got really different views on what’s considerate in this case.
Another landlord would hate washing in the bathroom or extractors being left on.