Avoiding "the every dyno is different conversation" I would guess that is about right.
Interestingly no-one rides it stock. I do not know anyone that hasn't done the prescribed muffler insert, intake manifold, jetting changeover that every Honda shop recommends. Generally speaking this adds a significant boost that most mags/pipe makers equate to roughly the 50 HP range.
When people ask me I usually just tell them "a lot"!
Honda's specs (which are not rear-wheel horsepower) state the XR650 has 43hp in stock trim, but with the optional power up parts (intake boot, exhaust baffle, air box restrictions removed, rejetted), they claim 55hp.
In reality, the bike has right about 50hp at the rear wheel with the power up parts.