What is Meant by "Eluting with 1-2% EtOAc/pentane" in Terms of Flash Chromatography?
Based on OP's question, I tentatively assumed OP is a novice to the isolation of organic compounds using column chromatography. Thus I'd explain this question with as basis as possible.

This paper OP sighted is for the synthesis of 2$H$-chromenes (2$H$-benzopyrans). They can be non-polar to polar compounds based on the substitution on benzene nucleus. The paper describes a series of relatively non-polar chromenes. When you do organic reaction, you monitor the progress of reaction with TLC analysis. During that analysis, you can determine that what solvent should be the most suitable for the particular compound elution. That's how the authours have determined several solvents such as 1% ethyl ether/hexanes and 2% ethyl acetate/pentanes, etc. for different different chromenes.

Some of these chromenes have been isolated using just one solvent. For example, evidently, they have mentioned isolation of 7-Methoxy-4-methyl-2-propyl-2$H$-chromene, using flash chromatography on silica gel, eluting with 2% diethyl ether/hexanes solvent system (this means solvent made by 2 parts of diethyl ether and 98 parts of hexanes, by volume). Note that it would also mean that they might have used certain volumes of following systems: (1) pure hexanes; (2) 1% diethyl ether/hexanes; (3) 2% diethyl ether/hexanes; etc. However, expected compound has come out with only fractions eluted with 2% diethyl ether/hexanes (remember, you supposed to analyze all the fraction by TLC), which may have combined and further analyzed by spectroscopy to confirm the structure.

As in another data set, they have mentioned isolation of 5,7-Dimethoxy-2,2-dimethyl-2$H$-chromene, using flash silica gel column, eluting with 1-2% EtOAc/pentane solvent system.It would definitely mean that they should have used certain volumes of few solvent systems: (1) pure pentane; (2) 1% EtOAc/pentane; (3) 2% EtOAc/pentane; (4) 3% EtOAc/pentane; etc. However, their expected compound has come out with fractions eluted with 1% and 2% EtOAc/pentane (concluded by the fractions analysis by TLC). 

Later Note: As commented by Waylander, these type of separation is called gradient elution. By the scale of reaction, total elution must not go over $\pu{100 mL}$ of solvent for each compound.