Who has inside information on what miners are doing now? Are they selling everything?
They can't be selling everything, you don't need insider information to understand this.
I can't agree with that. Mining farms are built with fiat. That includes building costs, hardware purchases, and backup generators. The infrastructure could be financed with loans. Loans have to be repaid, or owners may want to sell mined bitcoin to offset initial investments until the fiat breakeven point.
Further, you don't take into account that halving means that the miners' revenue will also be halved. But revenue is not profit, so, after the halving, they may actually begin suffering losses...
They will not suffer losses once the mining farm is operational. As long as the farm is mining, I can safely say that mined coins will always cover operating costs. Contribution to invested capital will be slower after the halving, but it is still profitable to continue mining.