That has not been their history. They have been eerily accurate in previous claims, as a NYTimes piece detailed.
ISIS is many things, evil probably the most prominent. But they are also very competent and professional. That is what makes them a dangerous enemy.
It is to soon to know if this is, in fact, either an ISIS run or inspired attack. However the killer obviously planned this operation well. That indicates a stronger possibility of their involvement.
Though to be fair, lone nut bars are capable of planning and executing devastating attacks on soft targets. Charles Whitman being the most relevant and comparable example.