No it isn't it's logic, I've yet to see 80m from any source French or otherwise(sorry but back it up with sources if you please), do you not think our press would be all over that? They even posed a question to the effect of "are you glad you got your business done early, how much do you think players like B Silva would go for now after the Neymar move?" to Pep, City must have leaked 43m themselves for our press to have taken that figure.
I even did a quick search and the only relevant result was a rumour about Bayern Munich preparing a 80m Euro bid back in March for him.
Edit: Ok you replied with one source(not sure how credible they are though) from way back in May... not enough to convince me sorry. The quote below is quite telling, seems more about their own opinion than anything anyone has told them:
I find it hard to believe our club would even bother bullshitting about one particular fee. It seems as though the £43m is unanimous with UK sources meaning it's come from someone at the club most likely as I said. It does seem low for a player such as him, maybe it was in mind with us also signing Mendy for a large sum as well and maybe there are add ons(although if there are it's surprising we haven't heard of them yet knowing our anti city press).