Interesting user situation.
Looking at the probable employer, I can certainly see why they might be a bit tetchy about security (critical energy/infrastructure, major global player, working in some very sensitive global locations). Although frankly I'm slightly surprised they use Trello...
I laughed and thought "would never happen to me!" and then I realised, that for really stupid reasons (understandable IT fuckups) I think several of my accounts have a backup linked to my employer, it is not impossible that something similar could happen. Hell, one of my food delivery logins is my employers (it rejected my personal email due to "existing account", then said no such account exists!".
In this case.. The ultimate confusion is ownership, the user opened the account, but settings were enforced by others. Tbfh, he fixed his own problem anyway.
I was never entirely sure how much "business data" to put in a free Trello account. Sure, it's probably OK, but WHO can snoop? I'm talking, Chinese/Russian/Korean/USA software engineers, who could theoretically have data slurps from bad actors looking for company Intel /R&D and secrets?