"The [HUAC] committee's anti-communist
investigations are often confused with
those of Senator Joseph McCarthy.
McCarthy, as a U.S. Senator, had no
direct involvement with this House
committee. McCarthy was the Chairman
of the Permanent Subcommittee on
Investigations of the Government
Operations Committee of the U.S.
Senate, not the House."
"The work of HUAC in the 1940s, while
not as wide-ranging as that under the
Senate Permanent Investigations
Committee under the chairmanship of
Joseph McCarthy, was the beginning of
the great search for Communists in
American life that dominated the early
part of the 1950s."
So no, the investigations by McCarthy were not part of the HUAC. He had his own organization, the Permanent Subcommittee on Investigations of the Government Operations Committee of the U.S. Senate, in which he did the same work. It's indeed a common mistake. However that mistake doesn't in any way reduce McCarthy's involvement in the "Red Scare". The investigations he carried out in the Subcommittee on Investigations were very similar to the HUAC, were at least as aggressive and were later condemned in much the same way. Encyclopedia.com considers the Senate committee investigations to be "more wide ranging" than the HUAC.