Flat tire without a puncture

Yesterday I went offroading, and did drive through some mud and afterwards some sand… When I got back on the paved road, I noticed that my left front tire was almost completely flat. So with the help of some friends, I installed the narrow spare wheel (max 80km/h), and today I went to a tire shop to get the flat tire repaired. They didn’t find any puncture, and told me the tire got flat because sand got in between the tire and the rim. They cleaned both and I’m back on 4 decent wheels instead of 3.5…

The technician was very good, and he told me it would be better to glue the balancing weights inside of the rim instead of clamping them on the outside. It looks better, it can’t come off as easy when the rim rubs mud or rocks, and it doesn’t sit in between the rim and the tire instead of clamps that help the sand to get in. In my opinion, Land Rover should use glued weights instead of clamped for factory fitted wheels.