It is. It's not so much an inductor (the winding is more just for convenience taking up the length), as a delay line.
Not really necessary anyway, as the length is under two nanoseconds, hardly a problem at 50, even 100MHz.
I like going overboard with transmission line transformers, because it's the most theoretically satisfying construction method, and isn't much more difficult than a conventional windup.
As a result, the phase matching in this design is probably good to 200, even 500MHz, though the transistors aren't nearly as good so it doesn't matter.
IMHO, it's less effort to design TLTs, than a conventional design that definitely will meet requirements. That is, a conventional one might poop out at 20 or 100MHz, and not have the right impedance, or have excess phase shift or imbalance or whatever. Whereas using TLT concepts it's just geometrically correct to begin with.
The notation for TLTs is kind of an abuse of coupled inductors; if it helps, redraw each set of inductors as a [set of] transmission line [pairs], and consider the EM waves (and port impedances) entering and exiting them.
Tim