[kenbellows]

It's not incorrect, but it is misleading. It's not so much that Catholics have a different Old Testament; it's more like they have extra Old Testament. Similarly, if you have a copy of the first edition of a book and I buy a second edition of a book with an added epilogue, it would be misleading to say that we have different books. The book are completely the same, but one has some extra content.

Again, it's not technically wrong, just misleading to someone unfamiliar with the topic at hand. In terms of relevance to the conversation, the reason it's misleading is that the moral codes and content present in the Protestant OT is all present in the Catholic OT as well; the Catholic OT has a little more, but by and large, they are pulling from the same moral background. Saying that they have different OTs in this context seems to suggest that this is not the case, and that Catholics and Protestants have a different set of sources for, e.g., moral guidance and teaching.