Why do you say that?.
This can be from multiple things, i've had it happen a couple times..
You could have inflated your back tire to much, and rode it, that it feels the need to come bulging out the side (most likely the problem.)
That tires really old, and that's a spot you messed up on taking your tube out, happen to rip a bit.. then inflating it just did the rest..
what i would do, is go to your bike shop.. by the Fit Tires.. 110 psi, i've rode 110 for so long, feels so much better than any other psi.. (personal preference.)

 my dirt mac2's have hold on for 5 months now whit out any problem, and i DO ride EVERY day.

 you didn't change the psi?

 well my bike has the 24'' versions, and i do change the psi depending where i ride, on dirt 3bar in front rear and in park 4bar on front 3,5bar on rear