The prophecy of Isa 21:1-10 is about the fall of the Babylonian kingdom to the Medes and Persians (Dan 5:28). The OP quotes an obscure version that poorly represents the Hebrew. Note the comments from the Cambridge commentary that better translates the Hebrew of V7:
- The verse reads: And if he see a troop, horsemen in pairs (1 Kings 9:25), a troop of asses, a troop of camels, then let him hearken,
hearken hard. This apparently is the expected sign that great events
are on foot; when the riders are seen the watchman is to listen
intently to discover who they are and what they are doing. The word
for “troop” means always “chariot” (usually collective); here it must
be used in the sense of “riding train” like the Arab. rakb. The
procession represents the Persian army. “Asses” and “camels” are
probably introduced as beasts of burden, although both animals are
reported to have been used by the Persians in actual battle.
The Pulpit Commentary offers a little more detail about the explanation:
A chariot with a couple of horsemen; rather, a troop of horsemen
riding two and two. This is exactly how a cavalry force was ordinarily
represented by the Assyrians. Chariots are not intended either here or
in ver. 9. They were not employed by the Persians until a late period
of their history (see 'Ancient Monarchies,' vol. 4. pp. 113, 122). A
chariot of asses, and a chariot of camels; rather, men mounted on
asses and on camels. It is well known that both animals were employed
by the Persians in their expeditions to carry the baggage (Herod.,
1:80; 4:129; Xen., 'Cyrop.,' 7:1, etc.). But neither animal was ever
attached to a chariot. Isaiah 21:7
Isa 21:7 is referenced in the book of Revelation concerning the collapse of the spiritual kingdom of Babylon in Rev 14:8 & 18:2, "Babylon is fallen is fallen".
The important matter here as far at the OP's question is concerned, there is no single rider on a camel or ass - it is an army.
The prophecy of Isa 21:8 was fulfilled in 539 when Cyrus finally captured Babylon at the end of the famous siege, some of the events of which are described in Dan 5.