An excellent conjecture, but not proven. Loewenstein's "Streets of San Francisco" (p. 46; https://archive.org/details/streetsofsanfran00loew_0/page/46/mode/2up) only says that it's a noble title and a surname. The street was dedicated in 1916 (https://bsm.sfdpw.org/subdivision/keymap/). The BOS resolution (https://archive.org/details/journalofproceed1916sanfrich/page/1192/mode/2up p. 1192 col. 2) does not mention etymology. The statue was placed in 1962 and the nearby bell, also commemorating Hidalgo, was placed in 1996, so the circumstantial evidence is not as strong as it first appears.