I have seen people cough hard enough to do some crazy things like pull muscles break ribs but even with vigorous coughing your grafts will be fine! That being said, even if some fell out...which they didn't...nothing can be done. No 5 second rule...
As said, coughing will not cause the hair graft to become dislodged. A more aggressive action would be needed for the hair unit to fall out. If the case you would have probably seen the hair follicle and the empty slit from which the hair follicle came from. As well as blood from the open wound. Which is obviously not the case.