I've always gardened where there is a lot of sand. Didn't recall that about the melons but sure seems reasonable.
Salt tolerance is pretty variable across genus and species. Living along the Atlantic seaboard, I've always been aware of what does better a few miles inland vs on the barrier islands.
I don't know what the soil is like in Libya. Of course I picture desert sand, but there could be many soil types. Even where I am, front yard is marl/clay and back is sand. I'm on an old marl pit, so the back is probably fill. I know there is a marl swale about seven feet down in the deep back yard that holds water for the area's most massive sycamore, looming over my house. Nothing freakish, but noticeable on aerial photos. What I'm getting at is there are variables everywhere. Do sycamores do fantastic in sand, or do they do fantastic with a deep swale of marl under sand with runoff water filling it?
So would Libyan sandy soil with little humus do well with the addition of saltwater beach sand? Would it do well with brackish water sand and sediment?
If the soil needs to be looser, sand could be a good additive, and sand with organic sediment would be even better. Sand with salt might be okay with adequate irrigation, but could burn roots and foliage of most plants that do not grow normally on beach sand.
I guess a lot more needs to be discussed or learned about the use of the sand, what soil type, and what is expected to be grown.