I could mod this as incorrect/misleading, but it's better to just reply with the correct information.
Boston is an anomaly when determining statistics of metropolitan areas. Unlike many larger cities like LA and Chicago, Boston has a fairly small land area. New York City is more than six times the land area of Boston for example. Whereas many metro areas grew over time, annexing adjacent cities and and towns, many of the towns in the Boston area resisted this move and were never annexed - They operate independently of the city proper. So while the Boston *metro* area grows, Boston itself has little room to do so.
That said, while there is crime in Boston (nobody would argue otherwise), your low statistic focuses only on Boston and not the Boston metro area, which includes places like West Roxbury, Dorchester, and Jamaica Plain, where the gun violence rate is much higher. To put it another way, using your statistic to make this argument would be like citing the murder rate in NYC based solely on the numbers in the Manhattan.