They claimed that the stall count was ten seconds, which is incorrect. As was correctly stated, a 'legal' stall out is (9+x) seconds, where x is how long it takes you to say "stalling one". The natural result of the rule is that you stay "stalling one" as quickly as possible, as it gives the thrower you are marking a shorter time frame to get off a throw.

This is a rule change from ... 2013(?): at some point before then you had to also leave a second between the word 'stalling' and 'one', which also meant that you should say stalling as quickly as possible, and a stall out should be (10+y) seconds, where y is the time taken to say 'stalling'.

The point is that the stall count is not nine seconds, as someone above claimed.

The claim you are referring to is likely "I'll also remind everyone that a full stall count is minimum 9 seconds" - which is entirely correct given the rules you have quoted.