Can the explanation of Tabby's star KIC 8462852 be an intervening planet in orbit around another star? Can an intervening planet in orbit around a nearby star cause periodic occultation?

Please excuse the crude text graphics:

Tabby ...... PlanetP ......................................... Earth
                |
             StarX



StarX and Tabby's star are close to each other (maybe part of some local cluster, like the Centauri brothers) so the line of sight with our Sun/Earth has maintained over the recent handful of years.
PlanetP orbits StarX with a period of around 750 Earth days.  Its ecliptic is at an angle (somewhat perpendicular) to the line of sight with Earth.
PlanetP's orbit rotates (precession?) a bit around StarX, so the amount of occultation of Tabby's star by PlanetP varies from 15% to 22% to whatever.
The answer is no, because the light curves simply do not match up.

Astronomers have detected planets before using the transit method. Large planets cause dips in a star's light curve when they move between their parents star and Earth; if these dips are regular and strong enough, we can conclude that there is a planet-like body orbiting the star. It's not perfect (best used on conjunction with other methods), but if there is a planet orbiting a star that is detectable like this, we should see a couple key features:


Periodicity, corresponding to the planet's orbital period.
Relative regularity in the depths of the transits.


Transits aren't always easy to see, but sometimes you can rule them out as the cause of light curves. The light curves of KIC 8462852 are one of these cases. Boyaijan et al. (2015) provided some of their light curves from the observations of the star. Here's one from Figure 1(b), showing a number of "dips":



There is neither regularity nor periodicity in the data, meaning that your proposed explanation is not possible. Looking at the dips in more detail (see the rest of the paper) confirms the conclusion.