I can see your point and I can see how you considered an array for third parameter. Is a list a parameter or a variable number of optional parameters? Could use some clarification.
You could check if there is a similar issue already raised on the FCC github. If not, you could open an issue yourself. Don’t expect an immediate fix but it will be considered time permitting.
Good to know is that MDN has excellent documentation on all the array methods such as splice() and that all the other methods are linked down the left side of each page. At this stage in the challenges it is a good habit to start developing a short list of go-to resources beyond FCC anyways.
You might not remember the gritty details of each and every one of these methods but it is good to know what is available and where to go to get the particulars when the need arises.
MDN also has similar documentation for Object, Map, and other built-ins too.