Strange magnetism of graphite

I'm not suprised that a pencil attracts a magnet. Pure graphite can be made by heating carbon powder, but it comes from mines. I recall that pencil graphite is also hardened by mixing it with clay ...and the magnetic properties of carbon depend on impurities as well as upon the crystal structure. If graphite from a mine has enough paramagnetic contaminants (such as ferrite, like lodestone,) it will attract more than it repels.
On the other hand, are you sure that the pencil carbon is acting weird? Some paint pigments are paramagnetic and will weakly attract a magnet. To assure that it's carbon contamination which causes the attraction, use some wire cutters to snip the wood off the graphite rod, then experiment with just the graphite. Perhaps see if the remaining wood and paint will also attract or repel from a strong magnet.
As a science project you could also try using a blow torch and a fire brick to burn off the graphite to see how much other stuff is left behind. Pure carbon burns into CO2, but pencil leads should leave behind some ash which is possibly magnetic.
Now if you want some REALLY diamagnetic carbon, buy some pyrolytic graphite from a science hobby supplier. The repulsion effect is so strong that a small flake of graphite will hover in space above a strong magnet pole.