Interesting experience on commercial airliner recently

I want to share an experience I had with my most recent commercial flight I took, to see if any of you would find any of what I say out of the ordinary. I'll leave out the airliner and any other identifying details.

My flight was a rather short one, under 2 hours in the air. I sat at the terminal and watched the 737-800 enter the terminal and everyone got off. From here, some of the normal stuff happened, the sanitation truck hooked up, and some ground crew did their usual whatever. At this point I started to notice something out of place. Toward the rear of the aircraft (about where the sanitation truck hooks up) a few workers gathered and we're looking and pointing upwards. They dispersed and then returned a couple minutes later with who I later identified as the captain/pilot. They talked and looked around at the area, then dispersed again except for one, who proceeded to slowly, very slowly, do a visual check of the rear of the craft, and slowly walked his way and looked over the entire left side wing's underside. Then there was another gathering including the captain/pilot under the belly of the craft.

I'll admit I was pretty nervous at this point, but they all walked away and didn't look concerned. Boarding started and I buckled up in my seat, one row up from the rear. As expected we took off on time with no apparent issues. Then the second set of very strange behavior occurred. The pilot walked to the rear of the craft shortly after take off, and was in the rear kitchen/galley area for the entire flight with two of the stewards, standing in a circle talking the whole flight. I was able to see this easily as I was so close. He walked back up front, and the announcement aired that we were making our landing approach. We landed without any apparent issue. I stuck around the terminal for a few minutes afterwards to see if any ground crew would go inspect the underside of the plane again but it didn't happen. We were the last flight that night though, so I figured maybe they would save any checking for later on or something.

So I'm writing this because, does anything sound out of the ordinary here? I can't help but think there might have been a problem with the aircraft that was noticed on the previous flight, and they decided to give it one more ride to see if anything would happen.