@Hughie_Jessel hi, this is normal as for renting your property you’ve probably registered your house as a gite business? And in France (like everywhere in the world) every business is taxed on its profit. Being a micro-entreprise the taxes are A/ lower and B/ a bit different but compare that to being self employed in the UK. I was self employed in the UK and was paying my taxes to the UK although being a French resident more than 6 months a year which makes sense as I made some revenues there.
If you want to dig deeper everything you need to know is there: service-publique. As a British resident you therefore pay the ‘prélèvement sociaux’ but not the national taxes (which residents are supposed to pay on top of these).
For information these ‘prélèvements sociaux’ includes (amongst other things) a cover in case of a sick leave (mostly in case of a liability to be honest) + a basic state pension.
Hope this was helpful, don’t hesitate to ask if you need more informations.