We say it pretty much every Friday of a MotoGP weekend: it's hard to draw conclusions from the first day of practice. The first day of practice is usually spent trying out different setups and then assessing which tires are the best compromise between performance and durability for the race, so just glancing at the timesheets doesn't tell you as much as you would like.
The first day of practice at Mandalika is even more complicated to unravel. First, there is the fact that it rained heavily on Friday morning, leaving the track damp at the start before drying out. Then there's the fact that nearly half the track has been resurfaced, the work finished not long before MotoGP arrived. Finally, Michelin changed the construction of the rear tire from the one used at the test, in response to the heat at the track, the new surface, and the data from the test.