First post here, just randomly picked this thread. To be honest the outfit in the second picture does look a bit special forces, but that said, I've never been one to stick to the conventional. And if all black with tactical boots is your thing, then rock it.
Lockstitch is so named because the two threads, upper and lower, "lock" together in the hole in the fabric which they pass through. The term "single needle stitching", often found on dress shirt labels, refers to lockstitch, as opposed to chain stitch which unravels easily and is usually used on lower quality garments.