I know other cards can give extra charges, but that's not what was happening in the cases I noticed, Vissegerd hit the table with too many charges. I've paid more attention to it since first noticing it, and I suspect what is happening is that 'boosted unit' is also covering units that have had armour added, maybe also units that have had other statuses added. Both unboosted units in my screenshot do have armour, and I think it was similar in the game that prompted my first post, and I have had a couple of games where he had the correct amount of charges.
Anyway, report made, thanks for the link.