Yikes, wonder if it was a similar thing to the Forrestal
I wondered the same thing.
Stray voltage on the rail?
Most aircraft have a weight on wheels (WOW) switch that disables the weapons circuitry (among other functions) while the jet is on ground. Although the SU-25 is way out of my experience, one would presume that similar fail-safes would be universal in all fighters worldwide.
On F4s (at least) a stray voltage check with a multi-meter was required to be accomplished on any station to be loaded with armament prior to loading and signed off in the forms.
Hard to say at this early stage.
Regards,
Sun