But relational frames are forms of relational responding that are based on features of the context (contextual cues) other than just the physical properties of the stimuli being related. We say that relational frames are contextually controlled because their occurrence depends on (or is controlled by) the presence of certain contextual cues. Contextual cues allow us to arbitrarily apply relational responses. That is, they allow us to make relational responses that are not based on the physical properties of the stimuli being related.
You arbitrarily applied a relational response to these triangles earlier. Your response was contextually controlled because it depended on the contextual cues you were given.