I don't think First Friday has anything to do with it. Earlier this year, May 8th was the External Solemnity of the Ascension; May 29th was the External Solemnity of Corpus Christi; and July 3rd was the External Solemnity of Ss. Peter and Paul - the feasts of the Ascension and Corpus Christi being on Thursday and Ss. Peter and Paul on Wednesday.
I have pinged jrny who is more knowledgable on this sort of thing than I am.
I think there are two points to make here:
1.) The first Sunday of October has, by special indult in the 1962 Missale Romanum itself, been designated as "Rosary Sunday". This designation dates back a while (not sure exactly how long) before V2. A maximum of two Masses of the Feast are allowed to be celebrated on the Sunday (one Low Mass & one High Mass), as is the case with any other external solemnity. One interesting case about this External Solemnity is that it is the only Feast ranked Second Class to have such a privilege; all other External Solemnities being of First Class Feasts.
2.) This year, since October 7th. is also on First Friday, the Votive Mass of the Sacred is not allowed to be said that day. Regardless of exercising the right of External Solemnity, the Feast always retains its Feast Day on its actual Day. Because the Holy Rosary is ranked second class and the Votive Mass of the Sacred Heart is ranked third class, the Votive Mass is disallowed, although a Commemoration of the latter can be done.
Point worth reiterating...External Solemnities do not transfer the observance of a Feast from its actual day. Such a concept no longer exists in the Novus Ordo, whereby Feasts are completely transfered to the nearest Sunday. But in the Tridentine Rite, a "Mass of the Feast" may be said on the Sunday per specific guidelines, while the actual Feast (Masses and Office) is still observed on its own day.