After wandering for quite so long as he had, he found it was surprisingly easy to remain in place and wait for someone to find him once he knew someone would come and find him. Unlike the Doctor, John was perfectly content to remain still most of the time.
Yet, as his attention drifted away from waiting into attempting (and failing) to translate the console controls, it completely slipped his mind that the woman who would find him to lend aid might be modern (or future, as the case may be) as the Doctor was, and thus as scandalously clothed.
As such, he forgot his manners once he turned to look at her. Rather than respond appropriately, he gaped, stuttered, and most probably flushed a deep red.