Perhaps this is because the report comes by way of another chain, for al-Haythamī himself reproduces it a page later with the wording:
“ … and the mosque of Muhammad ﷺ.” The remainder is identical. He then remarks:
“It was narrated by al-Bazzār. In the chain is ʿAbd al-Raḥmān ibn Abī al-Zinād; more than one scholar declared him reliable, while a group considered him weak. The rest of the narrators are those found in the Ṣaḥīḥ.”

Al-Suyūṭī records it in al-Jāmiʿ with the wording: “this my mosque and the Ancient House,” adding, “It was transmitted by Aḥmad, Abū Yaʿlā, and Ibn Ḥibbān in his Ṣaḥīḥ, and Ibn Ḥibbān signalled its soundness.” (1)

The ḥadith is further corroborated by a report from ʿĀʾishah that reads:
“I am the Seal of the Prophets, and my mosque is the seal of the prophets’ mosques. The mosques most entitled to be visited and toward which riding-beasts are urged are: the Sacred Mosque and my mosque. A prayer performed in my mosque is better than a thousand prayers in any other mosque except the Sacred Mosque.” Al-Haythamī states in al-Majmaʿ: “It was narrated by al-Bazzār; in its chain is Mūsā ibn ʿUbaydah, and he is weak.”

(It is the first mosque built upon the face of the earth, and Abū Dharr said: …)