It's not XOR.

Taking someone else's property can be both theft and conversion.

Conversion is a tort, a matter of a lawsuit between parties.

Theft is a crime, a matter between a citizen and the state.

The criminal equivalent of conversion is criminal conversion.

That article is confusing.

Someone cuts down trees from land they don't own to haul them away for lumber? That's clear theft to me.

Removing furniture that you don't own from a cohabited dwelling and storing it without telling the owner the location? That's clear theft to me.

Someone finds lost goods that they then keep for themselves without attempting to return them to the rightful owner? I can see that being something other than theft.