Your failure suggests no 'whole house' surge protector was
installed on the most common source of lightning damage - AC
electric. Lightning found earth ground via your modem
regardless of whether you had computer powered. Even worse, a
plug-in and adjacent surge protector makes this type of damage
more probable.

Even worse, a whole house protector on the AC would not have made a
bit of difference if the lightning came in through the phone line. It
still would have found ground through the PC just the same.