From a strict lore perspective, "No ship that small has a cloaking device!" is, in general terms, a true sentence.
The reason is that there were several less advanced versions of cloaking devices available to ships, but cumbersome, and not as effective and technologically advanced as the phantom one's.
The phantom's cloaking device was unique both in its design and in the use of the extremely rare stygium crystals. Those were what allowed its small size and extreme functionality.
So, our unfortunate captain should have said... "No ship that small has a cloaking device!... unless it is a TIE Phantom!!!"
To be fair classified project so he probably knew nothing about the phantom, obviously the security was high and if not for the events at imdar alpha the rebels and every one else would of been crushed by thousands of invisible fighters.
Also they were all destroyed by then. So it was technically an accurate statement.