Could a distant black hole (detected due to its mass) be in reality a Dyson sphere? When the black hole is only detected due to its gravitational effects on other stars and their light, could it be possible that it is in reality a working Dyson sphere?

It would still have at least the mass of the star but also blocks all the emitting light.

I got the idea from watching this Kurzgesagt video about Dyson spheres
The thing here is that a Dyson Sphere doesn't "block all the emitting light" -- that would violate the conservation of energy.  It does absorb the radiation from whatever body it surrounds and then re-radiates it.

As such, it's likely to radiate something like a relatively normal-looking blackbody spectrum, rather than the plasma X-rays from matter falling into a black hole, or the almost-nothing (thus "black") from a black hole with no infall.

As pointed out in @SteveLinton's comment the Dyson sphere would be much larger than the star or a black hole of the same mass in order to not melt, so at that distance the deflection would be far less, since it scales as inverse radius: 

$$\approx \frac{m}{r}$$.