He does have a creative mind, that is for sure, however, I don't think that when growing up, he had the opportunity to develop his creative side much...although he does need to use a bit of creativity at work.
He does bits of decoration around the house and I would say that 99% of the time I am fine with it. The 1% I don't like, I find it to be extremely tacky, but I understand that as a child he didn't have much going on culturally speaking...he went to a mediocre school, grew up in a mediocre village and was brought up basically eating crap food in front of a TV or playing video games.
He was touchy about taking it down because he says the stuff he put there are important and special for him. I am fine with it somewhere else in the house , but as said upthread, not where people are confined and cant look anywhere else. I think it is way too personal.
As for the house party, I am sure he would love it, h does like to entertain, however I would have to invite his family only as he got no friends...well, he did have one work mat that could become a close friend, but this guy changed jobs, so I can't see a friendship flourishing. He does go to the pub sometimes with work colleagues but I am sure is much more for the beer than for the company...
He has got an aunty who sounds like your friend when comes to decorating her visitors loo. Maybe he was trying to copy her? But the stuff she got there is way much more interesting than H's board and put together in a way that doesn't feel so personal.