The wording (as reported) of the agreement is that the French Language be "given precedence" in all "Ceremonies, billboards and pageantry"
That has been intepreted to include the official signing.
Nope, still can't find anything to back that up. Have you got a link to the report, or an image or something? Or any evidence of that being reflected in the official signing? Because I have looked, despite my reluctance to do the legwork when someone claims a thing which sounds a little bit unlikely, and I actually can't find anything at all to back up your statement apart from the moanings of a French minority group and some misleading
Daily Mail headlines.
As an aside, I understand that signage and texts at the Olympics is normally in three languages - English, French, and the host language so only two languages are necessary this year (
source). The French text of the charter is presumed to be the "correct" version, by the way, and French is listed first in the languages which are to be used... but there is nothing in either version which states that French must be used first and above the language of the host country.