Specifically this part:
Any funds you received after this will have been stolen by your partner.
If we are not able to detect te cheater peer, we only get the funds that were allocated by the commitment transaction broadcast by the cheating peer, right? So, if this is correct, what are this "any funds I received after this will have been stolen by your partner"??
Cheats happen when a party broadcasted an outdate version of the commitment transaction. It means the cheater shows you an old balance or the one that does not reflect the latest balance in the channel. With these action of broadcasting an outdated version, the cheater trick you to believe that they have a bigger balance than he is entitled to. This is called breach or a channel counterparty breach where the cheater can claim more fund that what he should have at the expense of the other party.
Here is an example:
For example, let's say the channel has a balance of 1 BTC and the other party has sent 0.5 BTC. The cheater can broadcast an old commitment transaction that shows a balance of 0.7 BTC in their favor, claiming the 0.2 BTC that they shouldn't have.
https://www.researchgate.net/figure/Lightning-Channels-Each-party-has-a-Commitment-Transaction-that-only-they-can-broadcast_fig6_304621007