The page does not show that the owl was a guard.
Known. A painted tomb has a large owl at the entrance.
The tomb is in San Pablo Huitzo, in Oaxaca, Mexico. It dates to around AD 600. It has an outer room and a burial room. The walls still have paint in ochre, white, green, red, and blue. The pictures show people carrying bags of copal, a resin used as incense. The owl's beak curves over a painted face.
Specialists are still learning who was buried here, and whether that face was a lord or an ancestor.
https://www.ancient-origins.net/news-history-archaeology/zapotec-tomb-discovery-00102475