If I may ask one more time just to be clear 100%. At this point, he would have to file tax considering 1099-R amount is regular distribution, the box 7 says '1L', he is in late 30's. Is there penalty involved as well?
Since he still have the option to pay the loan back with interest, the benefit of that payback is to increase his 401k basis, but that amount he puts back is none-taxable in the future, but the growth of the funds will be taxable in the future when withdraw occurs.
Thank you all again for educating me!