Depends...
From one perspective, the s-corp has a receivable from the other for the funds it paid to retire the LOC. = no taxable event.
From another perspective, you could argue that he took a constructive distribution from one s-corp and contributed funds to the other to extinguish the debt. Assuming there is sufficient basis in the first to support the distribution, this wouldn't be a taxable event. If there isn't basis to support this distribution, then it would be a taxable event.
~Captcook