This was intentional desecration.
Whether the action is specifically mentioned or not, the penalty applies.
UNITED STATES CODE
TITLE 18
Part I. CRIMES AND CRIMINAL PROCEDURE
CHAPTER 33 - EMBLEMS, INSIGNIA, AND NAMES
THIS TITLE WAS ENACTED BY ACT JUNE 25, 1948, CH. 645, SEC. 1, 62 STAT. 683
§ 700. Desecration of the flag of the United States; penalties
(a)(1) Whoever knowingly mutilates, defaces, physically defiles, burns, maintains on the floor or ground, or tramples upon any flag of the United States shall be fined under this title or imprisoned for not more than one year, or both.
(2) This subsection does not prohibit any conduct consisting of the disposal of a flag when it has become worn or soiled.
(b) As used in this section, the term ‘flag of the United States’ means any flag of the United States, or any part thereof, made of any substance, of any size, in a form that is commonly displayed.
(c) Nothing in this section shall be construed as indicating an intent on the part of Congress to deprive any State, territory, possession, or the Commonwealth of Puerto Rico of jurisdiction over any offense over which it would have jurisdiction in the absence of this section.
(d)(1) An appeal may be taken directly to the Supreme Court of the United States from any interlocutory or final judgment, decree, or order issued by a United States district court ruling upon the constitutionality of subsection (a).
(2) The Supreme Court shall, if it has not previously ruled on the question, accept jurisdiction over the appeal and advance on the docket and expedite to the greatest extent possible.