Adult grooming is a thing actually. Grooming isn't just specific to a child/adult scenario, it applies to any time a person is manipulating/intimidating an at risk/vulnerable person into doing what they want.
The groomer will look for ways to gain a victim's trust, often with gifts or promises. Eventually, asking for something in return.
In this case, he offered free dinners and money to try to get sexual favors.
There was already a huge power dynamic between them with him being richer, stronger, more powerful, etc.
With the main character being forced to pay a huge sum over an accident he was able to get him to agree to a contract where he exploits him sexually.
Grooming doesn't even have to be sexual either. It can often times be financial. The point is that the Groomer manipulates the victim to exploit them for something.
If you search up Adult Grooming you can find a lot of resources about this.
Like previous commenter said, grooming is not directly related to age, it is a type of relationship and can be age related or not.
let’s not water down these words ML is innocent but he is 22, that is not grooming