I think this can indicate whales and people generally are buying bitcoin than selling as they are moving their coins to noncustodial wallet.
Yes, that could be the reason, if we look at the numbers, from July to September, Bitcoin has been on the upside. Specially in the month of August, wherein we have a massive +25% increased in price.
I do not know of other exchanges, but what is happening on one exchange is also probably happening on other exchanges as usual.
As much as others might not like Binance because of CZ and it's other issue, we can say that it is one of the top exchange that we have in the market. So it might also reflect what is the actual picture as far as inflows and outflows of Bitcoins and what the whales are actually doing in the last month or so.