Going inside the ship to make his escape wasn’t part of his initial plan, but at this point he’s pretty much WINGING IT. If cutting through Sendak’s ship means getting back to the Atlas faster, then so be it. Not like he hasn’t improvised plans as he goes before.
Moving along the dark corridors stealthily but as quickly as he can, Shiro makes his way down through the levels with intent to leave from the LOWEST POINT that he can. Fortunately, most of the sentries seem to be otherwise occupied in the heat of battle, as there aren’t all that many moving through the halls --- yet he does still find a couple that are in his way. They notice him before he can duck out of the way, and rather than back away, Shiro charges forward. One of them is slammed against the wall, its head CRUSHED in an instant by his prosthetic hand. The other gets knocked to the floor and is promptly SHUT DOWN by a couple shots from the gun belonging to the first sentry.
Exhaling the breath he hasn’t intended to hold as the situation deescalates, the Atlas captain rises, tossing the firearm to the ground with a clatter. He’s not worried about being heard, though it seems that perhaps he SHOULD BE, as in lifting his head and turning to resume his hasty escape, he catches sight of someone down the end of the corridor who certainly hadn’t been there before. A silent curse and a twitch at his lip, Shiro wordlessly drops back into an offensive position --- he WON’T allow himself to be delayed any further. He has to get back to his crew and to his team, and there’s no point in hesitating when faced with a soldier, not in these circumstances.