This is an interesting article by David Cenciotti. He is a journalist with good knowledge on military aviation.
According to an authoritative source, two Su-27 Flankers escorted the Malaysian Boeing 777 minutes before it was hit by one or more missiles.
He doesn't say that at all, at least not in the link that you posted. He simply quotes his source as saying that
if Su-27s were monitoring/shadowing the 777 as it flew over eastern Ukraine, the Buk operators
may have mistaken it for a Ukrainian AF aircraft.
He (Cenciotti) also helpfully informs us that:
the operators inside the Buk could "read" the Boeing 777′s altitude and transponder and could easily identify the civilian plane enroute from Amsterdam to Kuala Lumpur
Really?