Did the sticker expire in March or earlier? If it’s March there’s really no way they know if it’s expired and should not have been towed or ticketed. If it’s earlier, well I’ve never heard of getting towed for that. I accidentally parked in front of a hydrant and didn’t notice for a couple days. I had multiple tickets (which makes sense and I paid them and moved it right away, I just didn’t check my car for a couple days after parking and I completely missed the hydrant in the yard). I can’t see how I wouldn’t be towed for that but you would be towed for expired plates. I’m honestly surprised I wasn’t towed! I had paid for my plate sticker when I got my ticket for expired plates, but it was the period between when they expired and when my new stickers came in that they ticketed me. That’s why I suggest putting that temporary printout on your dash (if you go the online route).
I would suggest calling the police non-emergency line to ask if you should have been towed or not.