No, Assyria only conquered Egypt in 673 BC under Esarhaddon, but the mention of Sargon is to precisely date when the oracle was given, not when it was fulfilled. In the fulfillment of the oracle, there is no mention of which king is doing the conquest, only that it is "the king of Assyria" and this oracle was fulfilled 40 years after it was given.
But that raises the question of why Isaiah had to walk naked for three years -- what is the three years for? It's unclear but one possibility is that the deportation would take three years.
Isaiah 20:1–2 (KJV)
1 In the year that Tartan came unto Ashdod, (when Sargon the king of
Assyria sent him,) and fought against Ashdod, and took it;
2 At the same time spake the LORD by Isaiah the son of Amoz, saying,
Go and loose the sackcloth from off thy loins,
And put off thy shoe from thy foot.
And he did so, walking naked and barefoot.
3 And the LORD said,
Like as my servant Isaiah hath walked naked and barefoot
Three years for a sign and wonder
Upon Egypt and upon Ethiopia;
4 So shall the king of Assyria lead away the Egyptians prisoners, and the Ethiopians captives,
Young and old, naked and barefoot,
Even with their buttocks uncovered,
To the shame of Egypt.
Here is the WBC commentary that provides some historical context:
1 שנה, “the year,” is apparently 712 or 711 B.C.E. Sargon has not been
active in Palestine since one year after Samaria’s destruction, 721
B.C.E., when a residual rebellion of Israelites and Philistines was
put down. Assyrian texts report that Azuri, king of Ashdod, withheld
tribute and tried to organize a coalition of states to rebel (ANET,
286, 249–62). This could well have taken place over several years and
may have included contacts with Hezekiah. This brought Sargon’s forces
back into the area. The Assyrian military action was thorough. Ashdod
and its allies, including Gath, were defeated. A new king, approved by
the Assyrians, was soon deposed by a Greek, Iamani. The Assyrians
intervened again, reorganized the government, and deported some of
their people, bringing in others from the east.
2 בעת ההיא, “in that period,” broadens the time span of “in that year”
in v 1 to make room for the “three years” of v 3. It is intentionally
locating the following events in the period immediately before the
invasion in 711 B.C.E. The words from God order Isaiah to act out a
prophetic sign, like Hosea’s marriage (Hos 1–3) and Jeremiah’s yoke
(Jer 27). The literal translation “spoke by the hand of Isaiah” is
most fitting. YHWH’s message is delivered by Isaiah’s actions: taking
off his clothes and sandals. השׂק, “the sackcloth,” is probably the
basic undergarment worn by the men. The text reports that Isaiah
obeyed. 3–4 A word from God interprets the sign that had now been
acted out for some three years (i.e., 714–711 B.C.E.). It is a
prediction that Assyria will conquer the peoples of Egypt and
Ethiopia, leading many of them captive back to Assyria along the
highways of Palestine. Political changes had occurred in Egypt during
this period. Shabaka, the Ethiopian king, consolidated his hold on
Egypt’s delta. The scheming kings of the delta cities who conspired to
keep the Palestinians in revolt against Assyria were gone. No
effective help would be forthcoming from Egypt in that period. 4 There
is no record of an Assyrian invasion of Egypt until the reign of
Esarhaddon. In 671 B.C.E. he defeated Tirhaka, occupied Memphis, and
installed Assyrian governors over local Egyptian princes. A second
rebellion was crushed by Ashurbanipal in 667 B.C.E. with Manasseh’s
participation. On this occasion the rebel princes were marched to
Nineveh, much in the way this verse pictures the march of captives.
John D. W. Watts, Isaiah 1–33, Revised Edition., vol. 24, Word Biblical Commentary (Nashville: Thomas Nelson, Inc, 2005), 321.
