I’ve spent a lot of time bushwhacking through scrub and low forest on small tropical islands. Yes, the going can be tough, and it might be slower than 1 mph in the worst cases, but I’ve never seen any place where I couldn’t have covered several miles in a day if I had to. (And the guy said he was resting during the heat of the day so he shouldn’t have been exhausted.)
Walking towards the sun every morning and away from it in the afternoons (or vice versa) should have gotten him to the coast in a couple of days. It’s really not hard to determine that.