It sold 300000+ in that timeframe before anime came out.ass class and particularly haikyuu got bigger boost.
Yes, it barely passed 300k while in the ranking before the anime. Now, it easily surpass 400k now; it is like at least 100k increase. That's big increase. It didn't got a boost like Haikyuu!! and AC (actually AC got push because of its movie); but it is still considered big boost.