When did Lacazette follow FCB on twitter? I don't think it matters much either way, Alex and Sam are great friends (went to a Rihanna concert together a few days ago before Sam starts with us on Aug 8th lol) on/off-field and since they won't see each other much anymore living in different countries, following their clubs' official twitters is an easy way keep tabs on transferred teammates because most players don't retweet official club updates much for their own followers to see.
Even looking (too) deep into into it and speculating he's putting himself on the radar which I don't believe but ok, like people above said it's unlikely we'd sign him or there would be buzz about it and looks like Arsenal is where most would expect him to land. He's a mature player and I doubt he'd be satisfied with the pecking order Denis and the next 19-23yr old striker we sign will have to be.