I've met people who are passionate about finance, usually they are traders though. I've never met a truly passionate accountant. But then I don't know many. I don't know how you would do accounting in your spare time. Maybe volunteer work?
I'm not sure if that was because they liked accounting, or liked helping people and had skills in accounting.
I could see "side projects" being interesting ways to interpret different tax laws with each other. As a "game" with a very large set of rules and formulas that occasionally changes in small but fundamental ways, I could see a certain type of person reveling in their ability to find interesting rule combinations ("loopholes").
Doing side programming because you get paid, or because you have an idea that you think could be useful or marketable later, yeah that happens.
Doing side projects because you want to learn a new language or tool, hoping it will make you more able to do your work better in the future, sure. That's a great reason.
There are actually a lot of good reasons to do side programming. But making that a big part of a hiring process is unnecessarily focusing on a behavior that is arguably not going to separate a good candidate from an average candidate. I'm sure there's a lot of really garbage side project code out there.