This sounds like someone hoping to get a gov grant but obfuscates the real issue: once detached from the mother ship the rocket still needs to accelerate from around 4-500 mph to 17k mph to reach orbit.
This not only makes acceleration easier, it also dramatically reduces the dynamic pressure on the vehicle at max Q, allowing for a reduction in the mass of the vehicle (making acceleration easier still).
It's difficult to make a rocket nozzle that works efficiently at the range of pressures from sea level to vacuum, at 50,000 ft atmospheric pressure is nearly 0.1 atm. Because of the exponential nature of the rocket equation even a slight increase in engine Isp can translate to a significant increase in payload (or decrease in vehicle size) or even cross the line of capability. For example, LOX/Kerosene engines tend to top out at a sea level Isp of around 309 seconds, though upper stage LOX/Kerosene engines have been built with vacuum Isps of 353 seconds. This translates to 17:1 and 12:1 mass ratios, which easily makes the difference between feasible and infeasible rockets (17:1 is at the edge of rocket building techniques, 12:1 well within it).