Balak tried to persuade Bilaam to come with him to curse the Jewish people. In 22:21 we find Bilaam finally agree to go with Balak's messengers, "וילך עם שרי מואב". As the story progresses, we read about how an angel stood in the path and the donkey had to veer off into the vineyard, while Bilaam was hitting it, the donkey spoke, Bilaam saw te angel and spoke to it.. etc. A series of very bizarre events.
Where were the Moabite officers during these bizarre happenings? What did they think of what was going on? They saw the donkey speak and did not think anything was out of the ordinary? Did they not see the angel - or did they think Bilaam was speaking to himself? They must have thought he was nuts!!
Maybe that is why the angel had to force the donkey off the path and into the middle of the vineyard. That afforded them some privacy so he could talk to Bilaam and so Bilaam could witness the miracle of the donkey speaking.