Sounds like good advice. A frozen ATL is a bit of a myth there is no such licence. A commercial pilot passes either the CPL or ATPL technical exams and then acquires a CPL with a Instrument Rating. To get an ATPL you need 1500 hours and to pass a multi pilot type rating. You must also have passed the ATPL theory exams. A Frozen ATPL simply means that you have obtained the CPL and IR and have passed the ATPL theory exams and are qualified to hold an ATPL, but still have to have the required experience and pass a type rating skill test. The licence doesn't unfreeze, you have to apply for the ATPL once you meet all of the requirements.
Once upon a time a co-pilot could fly with a CPL-IR and just the CPL theory exams. In order to obtain an ATPL the higher level set of theory exams had to be passed as well as meeting all the other requirements. Since the late 80s it has been normal for all commercial pilots looking for airline jobs to sit just the ATPL exams and hence the term "frozen ATPL"