Antiparticle is regarded as 'going backward in space-time'. For some fraction of time positron had been detected by Anderson in cosmic rays. Was it the result from future event?
What scientists mean by "a positron moving forward in time is same as an electron going backward in time" is that the mathematical expression describing the motion of the two particles is exactly same except for the direction of time. Reverse can be said, like you can say that "an electron moving forward in time is same as a a positron going backward in time". What they talk here about is the mathematical symmetry (of equation of motion) that come in while describing the motion of the two particles. That doesn't mean that any positron that we detect is coming from the future. It is just a mathematical description, and is not what happens at the observational scale.
The word antiparticle is surrounded by mystery. Note however that an antiparticle's antiparticle is the particle itself. Both have same mass and hence experiences same gravitational interaction. For example, under the earth's gravitational pull, both will fall downwards. The difference, however, is that all charges are reversed for the antiparticle (electric charge, baryon number...). The concept of antiparticle is an usefull one too, as in this way we can define what is a Majorana particle.
A Majorana particle is the one which is it's own antiparticle. It does not have any charge, and hence there is nothing to reverse under a particle antiparticle conjugation process. The familiar example of a Majorana particle being the photon, which is the same as anti-photon.
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