Yes, That video Clip was the Estrus Buzz, it was not an attempt at bugling at all. The sound is used when they are in search of the group, in this case the young cow heard an elk or group the hunter was imitating & this cow could not locate these elk & so was asking for their where abouts. It is not a breeding sound. This sound can be heard anytime of the year!
Wolf, no I don't have a magic method to force a cow into bugling! (grin) Like yourself I too enjoy hearing all the different sounds elk make & putting an identity to them, this helps a ton in hunting situations!
I will say cows will be bugle for the same reasons a bull would bugle to keep in contact with his present herd or harem. This bugling used by cows as bulls is recognized by the group members & instills this in them as they congregate with other herds or are getting too far away & cannot not be seen by the dominant cow. It can give direction & too will show the others of the group where the others are. Several cows can bugle at the same time yet be different enough that their sound is unique that it is known in an instant by those cows of each separate group. As pre-rut & peak-rut come into play this role is now taken over by the present herd bull. Hence, you will rarely see a cow bugle during these phases, it's generally done by the cows outside of rutting times!