Please note the final “or”. There is no requirement that you have been asked to protect the property, etc.
§ 9.43. PROTECTION OF THIRD PERSON’S PROPERTY. A person
is justified in using force or deadly force against another to
protect land or tangible, movable property of a third person if,
under the circumstances as he reasonably believes them to be, the
actor would be justified under Section 9.41 or 9.42 in using force
or deadly force to protect his own land or property and:
(1) the actor reasonably believes the unlawful
interference constitutes attempted or consummated theft of or
criminal mischief to the tangible, movable property; or
Good point, I missed that paragraph.
However, a 9.43 defense still needs justification under 9.41 or 9.42, if only property is involved.