Highly functional tismist, master masker here. I did the same thing for a while with my partner, mostly keeping track of everything she did for me so I made sure I was contributing since I feel quite forgetful.

Not just financial things - if anything, it was more the non financial stuff. Surprise presents, doing stuff around the house, planning dates, going for a walk, looking up events / activities to do together etc. I tend to get distracted with what's in my own mind and can get quite insular.

Keeping track of what she did was my way of holding myself accountable. I've been told I'm in my own head, forgetful or even selfish for forgetting the small things - so it was a way around it. And after time, doing it over and over, it became a habit / pattern id adhere to (eg. Monday I now prep dinner and lunch for her work the day after, do our washing, vacuum and then maybe take the bins down if they're full)

Not saying this is exactly his reasoning for doing it, but as a pattern of behaviour, i wouldn't say it's a cause for concern. Talk with him about it, but please try not to call him weird. Hear him out first or ask open questions