AP, DAP, and AP+NP-NP are all soluble in toluene. Practically, technical-grade toluene contains very little water & the authors deduced that traces of water in the solvent interacted with the product without contaminating it.
The reason for using toluene instead of alcohol (such as methanol) seems most likely to be related to the fact that the technical-grade alcohol will contain more water & also the lower volatility of toluene has served in getting the desired crystals of the size required.
In a good solvent for recrystallization,the compound should be soluble at the boiling point of the solvent and only sparingly soluble in the solvent at room temperature. They might have tested several solvents and found out that toluene gave the best crystals.
beside to all the above reasons toluene consider more safe dealing than methanol. and have relatively physical properties similar to pyridine derivatives .