I guess I did, oh well, so how about it, why would my large cargo ships be the only ones involved in a battle at the planet they are at when none of the other ships were included in the battle?

Select a planet from the drop down menu at the top of the page, then click on "Fleet" from the menu on the left.
This shows any fleet that is stationed on that particular planet.

An alternative way is to click on "Empire" from the menu on the left (Does not matter which planet you are on), scroll down to the bottom of the page until you come to the fleet section.
Each column represents the planet/moon and the row the fleet type. The table shows which fleet is stationed at which planet and also the amount.

Any fleet which is stationed at a planet will automatically defend that planet when it comes under attack.
If a fleet is on route to another planet/ moon it will not come under attack as it is not stationed on a planet/moon (Also known as fleetsaving)

Your fleet (except the large cargoes) may have been either in flight or stationed at another planet and hence would not be included in the battle.

ah no they were not on a mission they were as they are now still stationed at the planet. If they were on a mission I wouldn't be asking this question

Maybe you had LCs queued in your shipyard at the time of the battle and they finished building afterwards. Did you check the combat report to see if the cargoes in question actually were not involved?