There are some turbine engines that should have some avgas run in them periodically-or at least there used to be. Don't know about the PT-6. However, just cause you know that they can, unless MX tells you to (most line guys don't check the logbooks to see how long an engine has been run on avgas) you probably shouldn't be doing it.
Sounds like you phornicated the canine and are just making excuses. I'd guess that you were supposed to be putting the proper rated fuel in and now are cya because it didn't blow up.
Line guys are human and screw up on a regular basis just like everyone else.
Once in a while you find one that is man enough to admit it...if you're lucky!