"We have tons of important meetings with Members of Congress today. But [Julian] and I also stopped to take a photo outside the door of a member we are not meeting with," Housefather wrote on Twitter.
Santos is facing widespread calls to resign after he admitted to lying about his work and education history during his congressional campaign last fall.
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The snipe from America's neighbors came just hours before Santos would have a tense exchange with Sen. Mitt Romney, R-Utah, on the floor of Congress as Biden was about to speak.
"You don’t belong here," Romney appears to have said, in full view of C-SPAN cameras. "You ought to be embarrassed."
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Romney goes on to call Santos an "a--," to which the lawmaker responded, "You're a bigger one."
Santos secured himself an aisle seat sure to draw cameras as lawmakers, Supreme Court Justices and President Biden entered the room. Photos showed he had been shouldered out of the way by the time Biden himself came into the chamber, however.
U.S. Rep. George Santos (R-NY) waits for President Joe Biden's State of the Union address during a joint meeting of Congress in the House Chamber. (Win McNamee/Getty Images)
U.S. Sen. George Santos (R-NY) (R) watches as President Joe Biden greets members of Congress after his State of the Union address. He had been pushed out of his aisle seat before Biden entered. (Drew Angerer/Getty Images)
"He’s a sick puppy, he shouldn’t have been there," Romney told NBC News reporter Frank Thorp after Biden's speech. "Given the fact that he’s under ethics investigation he should be sitting in the back row and being quiet instead of parading in front of the president."
Fox News' Lawrence Richard contributed to this report.