That's either a lie, or just poor record-keeping. I would find the poor record-keeping entirely believable, but besides the point: even if they _had_ been trained to use flashbangs, then they we not trained properly or the shouldn't have been used at all.
Just because something is standard procedure doesn't make it the correct procedure.
I'd be more inclined to believe it was poor record keeping if there wasn't a decades long history of police lying to cover for each other. Fool me a thousand times...
I'd be worried about confirmation bias on that front. You don't remember all the times they told the truth but just did a poor job. It sounds like a lie either way.
But in my experience in the military, record-keeping is boring and routine, so there is a tendency to just pump out sub-standard paperwork and say "nobody is really going to look at it anyway, and if they do, they already know it's not reliable."
Training records? Pah. I'm surprised they even have training records. It's probably just a speedily-drafted form with a signature line on it. That's how you train 45 people at once: you make one form, have them all sign it, then you do the training. The form isn't accurate? Who cares, you got the signature and 'did your job'.
Just because something is standard procedure doesn't make it the correct procedure.