The idea behind this statement, which is commonly made about the relationship between these two cultures, is that the Greeks were the ones who came up with all the ideas. It is said that the Romans simply copied them. That is the meaning of the part about innovators and imitators. The part about practicality asserts that the Romans were not interested in philosophy or other abstract thought.
This idea has come down to us in part because many aspects of Roman culture seem to be derived from the Greek. For example, most Roman gods have counterparts in Greek mythology and so people tend to say that the Romans got their gods from the Greeks. Another example of this sort of idea can be seen in the following quote from the occc-encyclopedia link:
The influence of Greek culture became pervasive, and wealthy Romans began to affect the leisured style of the great centres of the Hellenistic world; see Hellenism. Architecture and the visual arts flourished, as the Romans imitated all the trappings of Greek civilization. One of the results was the development of Roman literature on the Greek model, including drama, epic poetry, and, not least, historiography.