I did two 5M runs on a treadmill faster than that pace this fall (last 5M of 8M in 25:52 and last 5M of 10M in 26:08) and was not in particularly good shape all fall, and each time I would have finished faster but the tmill was capped at 5:00/M max. So, unless he was going much faster than that for the latter half of the run, I'd say he's probably run-down, sick, or just getting started again with his training.