It can be, if used as a whole-house (or whole-apartment) filter. There are three sets of connections on the filter, and each one can be connected either via the bare wires (on the left side) or the phone jack (on the right side).
The way he's wired it up is:
Line (input from Bell): directly wired
Modem (output to modem): RJ-11 jack
Phone (output to home phone wiring): RJ-11 jack--
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