$chan is the identifier
.topic or .mode is the property
You have to use the property with the identifier to get what you're wanting, as is the case with a fair number of identifiers that have properties.
I suppose it's possible for Khaled to have made a different identifier for each property, rather than a single identifier with a property extension (for lack of a better term), but as he didn't, I'm going to suspect that there's a good reason.