This distinction is emphasized and reiterated repeatedly, and overtly, in order to justify protestants’ attempts to
evangelize Catholics–as if we didn’t already have the Good News (and as if they didn’t take…or raather, get…it from us…).
Protestant pastors have a (mostly) unwritten rule amongst one another, against targeting sheep of another protestant pastor’s flock, regardless of denomination. The rule doesn’t apply to Catholics, because that’s the
See from which they all fish.
Notice how many television or radio evangelizers will refer listeners/viewers to “…a good
bible church, or bible based church”. (–that would be code de jure, for ‘protestant church’–any protestant church…just not a Catholic church…).
The question is frankly, patently insulting, and everytime I’ve been presented with it, I’ve treated the person posing the question to a Catholic cathechesis on Church history.
Politely, of course…
Mary: Of course!

I had a LCMS Pastor friend and a Baptist Pastor friend and the
Baptist Pastor used to say
jokingly he received “bonus points” for converting Catholics. The are not “off limits” as you say regarding stealing sheep.
Pax Domini sit semper vobiscum.