$+() is a concatenator: A $+ B can also be written as $+(A,B)
$(A,N) evaluates its argument(A) N times.

So

$( $+(%,channel.,$chan) , 2)

evaluates $+(%,channel.,$chan) 2 times, as follows:

0: $+(%,channel.,$chan)
1: %channel.#chan
2: *!*@host

Sais