I think the relevant part is that one definition of "defund" is (from Google answer box/featured snippet, only provided definition):
>prevent from continuing to receive funds.
So some people upon first hearing the phrase "defund the police" understand it to mean "prevent the police from continuing to receive funds". Without any qualification, this is naturally understood to mean "all funds", which is not the concrete policy proposal behind (what seems to be most uses of) the phrase.
I myself had this understanding of the phrase "defund the police" when I first heard it (which is not something that I would support) but I do support most of the concrete policy proposals behind the "defund the police" movement that involve reallocating funds from the police to social services and other programs. I would be hesitatant to use the phrase myself though, because this interpretation seems quite common among people not "extremely online".