you may contact Gatwick airport with messenger (there is a button available on their website) requesting to send you the list of flights on July 8th.

Their website only shows today and yesterday's flights only but they might be able to provide them on a specific date. So if you were able to see that other Easyjet flights took off on the same day and around the same time, the weather excuse is BS. The airport may also provide you info about weather and cancellations too.