Not at all.
By the 17th century they'd grasp instantly they were seeing skirmishers operating in loose formation. Good for covering ground and seeking out cover and concealment. The clothing makes that abundantly clear.
They'd wonder why they don't seem to fear cavalry, why they aren't mounted, and how they stay in communication without riders and messengers.
Radios, motorized transport and rifles would explain that quickly. They'd seem unfair, and like magic, but given some time even Alexander the Great could grasp the logic of it, even if he wouldn't agree until he'd seen just how effective it was.
They'd be surprised, mostly, at the level of discipline and training that the modern soldiers show. Used to skirmishers that had to be ready to run and hide at any time to escape being attacked by cavalry or trapped by a real infantry formation that would tear though them like tissue paper, they'd be shocked at watching modern troops dig into the landscape and any scrap of cover like ticks and repel even massive human wave attacks, or cut down cavalry in a moment.