That's extremely unlikely. Working with cancer cell lines will not give you cancer - it's non-transmissable. (with the exception of Tasmanian Devils, and one recorded case of maternal -> fetus transmission).
The cancer that he had was clearly his own, as evidenced by the fact that they were able to match up his normal genome with the tumor genome and find the handful of differences that were driving the cancer.
*Full disclosure: I work in the Genome Institute at WashU, where this sequencing was done, and while I did not work on this particular case, this sort of cancer genomics project is what I work on all day long.