You got the rough idea. The two different flavorings could be in completely different bases. If one is a PG base and the other is... not PG but VG in combination with other ingredients... Depending on the percentages it could mean, let's say..., up to a 20% difference in the total PG level between the two liquids.
I've found that some places can be rather sloppy when it comes to telling you the real percent totals in their liquids. Often times if they say their liquids are "50/50" they are naively telling only the percent of their base liquids, leaving the amount of PG or VG in their flavorings completely out of the equation.