Randall,
I bet that the shot of him coming back to the dugout is after the at bat, and that he didn't take the field in the bottom of the inning. The NYTimes article from the next day makes a mention of Mantle having a sore right knee and ankle, and Houk only wanting him to take one swing that day, and only one the next. However, since he wasn't put in the next day, I guess he wasn't doing well enough to take that last swing. I would gather that no big deal was made of him coming back to the dugout after the pop out on the 28th, being that he played the full game the day before (though there is mention of him receiving a standing ovation during his first at bat of THAT game). What you probably have there is the final moment that Mantle was on the field during a game.
It's too bad we can't find out for sure whether the PA made an announcement when the Yanks took the field in their half. So of course, this is all just conjecture, but in my head, it seems to make some sort of sense. Then again, I just got back from the gym and my brain is noticeably fried.
Graig