Platoon

They're the rear detachment of a much larger deployed unit. They are what is left over of their platoon, or the combination of the remains of a couple other platoons. You're right that by size along they would be a squad, but with Rear-D the organization isn't always perfect because you make due with whoever you have. IRL they'd probably be combined with Jill's platoon and have less interaction with the Sergeant Major than we see because there would be someone who outranks them representing even more pieces of the Rear-D. For one of my deployments the battalion of 800 had a rear detachment of around 50 with a Lieutenant in charge. Those 50 were split into four platoons of about a dozen, but self-identified as being companies because they were the remains of their companies that had deployed.