retune for lower emissions

Following a BT openreach van today and it had a sticker on the back saying that this van has been retuned and now had 27% lower emissions. Do they mean remaped?

I think it's mostly fiction.

If you could remap them to be that much clean, then they would use less fuel and be in a lower tax band.

Wouldn't the manufacturer do it in the first place?

Or they have adjusted the throttle cable so they only have half the travel, on a similar note I was behind a van (royal mail maybe?) that had a sticker stating it was limited to 70mph I thought that comercials had a max of 60mph?

70mph on a motorway up to 3500kg, 60 over that. 60 on a dual cabbageway, 50 on a single. Same as a Hijet.