Most likely what you saw is "brood food", nurse bees excrete it from special glands to feed young bees. Its the bees form of baby food. Sometimes when we pull out frames and damage cells both capped and uncapped the brood food pours out from the cells as well as the squished little bodies of brood. Its more obvious when bees put drone brood between frames and they are damaged when pulling them out.
Its no problem. Next time just gently replace the frames and the bees will clean up the mess. One thing you can do to help with less damage to brood is to break apart the hive boxes before pulling out the frames. It makes it easier to lift them out. Try and start with taking out frames 1 or 2 as they are less likely to have worker brood to damage (but may have drone brood this time of year). When you are done inspecting and the frames are all back in, with 2 hives tools push the frames snugly together centered in the hive body. This also makes it easier to do inspections without damage on your next visit. It gives you room to push the frames out Its especially helpful when running 8 frame equipment as it tends to be a bit wider.