maybe a clearance for the approach does clear you to descend at your discretion implicitly
I wouldn't go that far.
My reading of the text is when cleared for approach, you are cleared to descend while still observing the higher of MSA and approach altitude restrictions. After the IAF for sure at least (see second part of the post for before the IAF...).
In Spud3 case, the MSA is 2700ft in the north east until 18M then 2100ft everywhere else. The initial and intermediate approach are published at 2500ft. So, you may only descend to 2700 then 2500ft or 2500ft directly (depending on your arrival sector) and never below until you pass the FAP.
After thinking a lot about it, in this particular case I'm pretty sure the ATCO implicitly allowed further descent (to confirm, Spud3, it would be great to tell us what where your following actions and interactions with ATC).
Now in a more standard way, I'm pretty sure the approach clearance should come with a level/altitude UNLESS the last assigned level/altitude is compatible with the approach profile (meaning you won't go below that level before somewhere between the IAF and IF because of restrictions). Here FL80 is clearly not compatible since at KELON you should be FL050 max.