Tis_Bearself:
No one is “investing” in the Church so this is not an issue of paying customers being misled. There is zero impact on society from the Church defining member in this way.
Would you agree that we generally assume the weight of an organization is often proportional to its overall membership. A political party with 20 million members carries more weight than one with under a million. A threatened strike by a large union can have far more impact than a smaller one. By inflating numbers it inflates its perceived standing in the community.
Plus there is another impact to consider: Those individuals who are credited as being Catholic but are not in line with it would strongly prefer not to contribute (mistakenly) to that final total. You may dispute that, but back when it was revealed that the LDS were performing baptisms for the dead there were some who not pleased, including some Catholics.
If somebody doesn’t want to believe how the Church defines members, they’re free to not believe it and it has no impact on them.
It’s not a matter of belief or disbelief, but of being led (purposely?) to an erroneous conclusion. It only takes a few extra words to make clear to any reader that the number is specifically the number of people baptized as Catholics irrespective of their actual faith. To make people think an untruth is bearing false witness.