Nope, not true, fish for all the white bass from a boat all you want.
Technically speaking you could get into trouble if you were say fishing for a species where the season was closed on that body water, like walleye on the St.Croix right now, or walleye, bass, northern, musky on the St.Croix or any lake in MN right now.
Now, I suppose if you were draggin lindy rigs with leeches or minnow on the St.Croix right now, and a CO came up to talk with you, even if you honestly and truely were fishing for white bass or panfish, you may have a lot of explaining to do Since you can’t even target fish that are in a closed season, and IMHO it would appear you are fishing for walleye, so be aware some tactics are probably not the best choice to use when the season is closed. Apparently it’s the CO’s descretion wither or not you are targeting fish out of season and wither they would ticket you or not, I’ve never really seen or heard of a CO pushing the issue, but it’s somewhat of a concern, though I wouldn’t put it pass them to ticket you and let the courts figure it all out.
That may be more of what they were talking about, make sense?
BTW the MN DNR has good email support, if you email them during the week they are generrally pretty quick about getting back to you.