hm, can't it simply be coincidense??
Maybe there is no such thing as a bruised player in BB, and then there is no need for your suggestion.
I think you just got unlucky, but if the calculator chose an other player for the injury he would have gotten the 4 weeks as well...
The bigger problem is there is a complete absence of balance with injuries. It is not just the fact that the season is 14 weeks with 2 to 3 games a week, so that long injuries can cost you half of the season. Also, with the current speed of training, an injury like that sets you back 2 levels or more on a trained player.
"I don't know half of you half as well as I should like; and I like less than half of you half as well as you deserve."