Burchett did not say this briefing was in a SCIF, but SCIFs are required by law and policy for TS/SCI level classified briefings–and when Burchett speaks of a briefing about extraterrestrial life that "would have set the Earth on fire" and "unglued" the country if released, we can almost certainly conclude such a briefing would sit at the TS/SCI level at minimum .
As an aside, any UAP file that involves intelligence collection methods–radar systems, satellite imagery, signals intelligence, reconnaissance data–is automatically TS/SCI because it reveals sources and methods.