Not necessarily. Tim Horton's donut shops are ubiquitous in Canada (and even in the Buffalo-Niagara area)- not unlike McDonalds in other parts of the US. If that is the only common bond between the man and his group, then it is a tenuous bond indeed. It really doesn't make that Tim Horton's self-immolation any more or less likely to be a terrorist incident without evidence of a further connection.
Please find me the name of this tragic victim if it has nothing to do with terrorism.