It is only about fifty centimeters high and so, its cape is very small. As the local people state, it is a "caption" - a little cape. There is a local expression in use which says -"echar un capote" which means literally "to throw someone a cape" and which has the meaning - to do someone a favor, or to help someone out. The image clearly comes from the bullfights where the assistants of the bullfighter sometimes need to come to his rescue and they distract the bull with their capes.
The "little cape" of San Fermin is believed to do some "miraculous" favors for some of the runners who inexplicably come out unscathed from some very dangerous predicaments during the running of the bulls. That explains why each morning of the running of the bulls in Sanfermin fiestas, the runners sing the homily to the figure of the saint, just before the start of the run. The words to the song in translation go something like: "we ask San Fermin to guide us in the run, as he is our Patron and we beg a blessing from him." Learn Euskara version.
And it often seems more like a miracle than just pure chance, when we see runs avoid dangerous moments that occur during the running of the bulls. Regularly there are impossible situations where runners come out unscathed that seem only possible to explain by referring to the "little cape" at work yet again.