So yes, Ukraine probably knew they had low altitude anti-air assets, however the higher altitude attacks only started 2-3 days before MH17 was hit, so if Ukraine knew they had a Buk it was not until later on, not during June like you are claiming.
He's right and wrong, it's true that high altitude shootdowns only started three days before MH-17 was shot down, however Ukraine did know the rebels had Buks back in June, because it was in June that the rebels captured Ukrainian Buks.