This is a system of Bitcoin. The Bitcoin prices go up and down, that is not a unique thing.
This is the best time to sell Bitcoin and when it will go down so buy Bitcoin. This is the system of Bitcoin and cryptocurrencies.
Anyway, Bitcoin prices are like a peak of mountains. Let's see that Bitcoin price goes down in October or not.

I would consider this the worst decision or advice this year. we are 2 years into bear season and it is almost over and there is no reason for us to sell our bitcoins now. moreover, what do you rely on to be confident that bitcoin will fall again to buy bitcoin? if you sell it now and the price doesn't decrease but continues to rise, what will you do? Would you sell bitcoin for $27k and buy it for $30k?
Yes, no one can predict what prices will be like in October, but there's also nothing to say prices will drop. the idea of selling now is a bad idea if you are only selling out of fear and not because you need the money for an emergency.
I think he may be suggesting it can better to sell now for buyback later at lower prices. Some people (including me) like this method to maximize our profits. But I would agree that its very risky as you describe, selling at 28k may mean buyback at 30-35k later. But still I think October is never better bitcoin month historically. I feel like bitcoin price will only increase when fed will start to ease its monetary policies. So we need to wait some more month(s). Next year will be much better than 2023.